The quick answer to your question is, "Yes".
It's a fantasy oriented system, be it D&D or Pathfinder. - You're supposed to be able to things like this, but it all comes down to your character's ability, wealth, power, and influence.
I would simply look up, google, Pathfinder SRD (this is a Pathfinder/Paizo site, afterall) or d20 SRD.
The section you're looking for, as far as price, is "good and services". Towards the end, you'll find prices for spellcasting.
Keep in mind (and in either source, the text will warn you), spellcasters generally do not like to leave home to do this sort of work. A spell that you can get (eventually) cast in town for a reasonable price may cost you more to hire a wizard to cast on site, if they're willing to do it at all.
As far as binding an earth elemental, you're going to need spellcasters with Protection from (good/evil/chaos/law) type spells, some form of planar binding or gate spell, and an appropriate bribe to give the elemental.
Elmentals and outsiders don't work for free. You need to be able to make a contract with them. (Spell rules text in either SRD will pretty well cover this.)
(EDIT) Removed some extra text, was going to go in depth but figured that being able to look up the SRD's would make the job easier in the long run.
If you are using the Kingdom Building Rules in Ultimate Campaign.
Construction: Construction is completed in the same turn you spend BP for the building, no matter what its size is. A building's benefits apply to your kingdom immediately. At the GM's discretion, construction magic (such as lyre of building, fabricate, or wall of stone) can reduce a single building's BP cost by 2 (minimum 0). This is a one-time reduction per turn, regardless of the amount of magic used.
All available in the PRD.
Will go in for a bit more detail, then.
1) You're going to have to narrow down the location as much as possible. Has your party already 'liberated' a suitable location from a less than willing opposition force? Are there other civilization centers nearby? What material resources are nearby? What kind of terrain is out there between your soon to be settlement and the nearest population centers? Are there roads?
It doesn't have to be insanely specific, but a good overall idea as to who/what/where will make the next step a lot easier.
2) You've established that you want the good mountaintop fortress, and maybe having the city within the mountain, nearby caverns, or maybe in the valley/plains surrounding the area.
Next step, here, is trying to determine the sort of culture that you want to foster.
If you want to have a very hardy and battle efficient people, it's hard to beat Sparta.
It was illegal for anyone of the upper classes to engage in trade. Everyone of sufficient rank had an army of slaves to generate income. The only people allowed to trade were an underclass of seedy merchants, and even then only with coins that had been deliberately quenched in pickle brine in order to prevent the metal from ever actually having any real value except as a trade token within Sparta.
This pretty much guaranteed that the Spartan culture remained isolated from other cultures, except for those Spartans that were sent off to war and forced to come to grips with foreign methods.
3) Once you've established the sort of culture you want to foster, you've also established the kind of industries that you want to back. - If you want a war like people, obviously you want to have industries and trades to support the method of war you intend to wage.
In your case, you're going to /definately/ need an army of farmors to keep the mountaintop forest in food. You're going to need a good supplies of millers, bakers, brewers to make the staples. You're also going to need several competent alchemists to make sure you can store a bunch of supplies against the onset of siege as an example.
Don't neglect road building and bridge building. You can't have a decent sized populace without defense, and you can't have an effective and economical defense without being able to get the relatively small number of garrison troops from place to place.
5) Now, back to the original purpose of the post.
a) If your character is in good terms with the Dwarves. USE THE DWARVES. You will probably benefit more from throwing the Dwarves a cushy kickback than you would by snubbing them and hiring some random spellcaster to get the work done in an instant.
There are few things worth to the Dwarven Psyche than failing to give a task the appropriate respect, by taking the time to do it right. Digging a giant latrine? Use a spell. Creating a cavern destined to become the chambers for your church or great hall? Use the right aritisan.
b) Taking aside the above, don't be afraid to use spellcasting where spellcasting is due, just be aware that the costs can mount up... fast.
Building a moat? A "move earth" well is a decent option. As a 6th level spell, it'll cost somewhere around 3,300 for a scroll or 990 gp for a spellcaster (assuming one will do it for minimum book price), but can move 5,565,000 cubic feet of dirt around in four hours time. (compare that against how much dirt a ditch digger can move around in 4 hours with a shovel, and "move earth" becomes rather economical)
Opening up the mountainside? You're going to be a bit dispointed when you start looking at "transmute rock to mud". A standard scroll will run something like 2,250 gp or 675 gp direct from the caster. However, that will only net you 9,000 cubic feet (18 10x10x10 cubes) of rock that still has to be flushed out of the cave or hauled out. It'd be enough for roughing out your lordly chambers, but pricy to build the entire fortress this way. - Dwarves would probably be cheaper.
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There are definitely ways to accomplish this, but you're going to need to take a holistic approach as much as possible. Sometimes having allies take care of it needs you better rewards in the long run.
You tend to get people to like you more when you owe them favors, more so than when they owe you favors. (So long as you're not a complete welch or deadbeat that is) If you work with others when you /can/ instead of when you /must/, you might build connections that your community wouldn't otherwise have.
Outside of that, the Paizo Ultimate Camptain book or the even the old old D&D 3.5 Stronghold Builder's Guide (the only reason I refer to it at all is that it sticks to the topic of building strongholds, where Ultimate Campain covers a few more topics) - I would read Stronghold Builder's guide for ideas, but use Ultimate Campain for the mechanics (personally, as I access own Stronghold from before converting to Pathfinder, and have access to Ultimate Campaign in my group)
so there's a big wall of text OS_Dirk just posted that I'm not sure answers what you wanted to know.. or there's the kingdom building rules in ultimate campaign that do. The kingdom building rules are designed to let you not worry about who/how things are being built - you're a ruler, you could care less about that level of detail. You simply command them to be built, and they are. Carry on to the next month and do so again.
<quote>Edit 2: and i would actually like to go as in depth as possible with this. i understand i am asking alot with that. but we have alot of casters in our group. this is stuff that could apply to almost everyone in my group. so the more in depth we can get into city building with magic the happier i and im sure my group will be. and of course anyone else who is interested in this as well.</quote>
True enough, CraziFuzzy, I put down a pretty large post. - Just put out the sequence of events as I saw it, to give food for thought.
If the Ultimate Campaign build rules are enough, awesome, it can save a lot of worrying about the logistics.
In my experience, though, nearly any player that ends up with good chunk of land starts off as a lowly adventurer "purchasing" that plot of land at the end of a sword.
In some cases the logistics end up determining what kind of Kingdom you're going to be able to have.
As an example, in one of more recent campaigns I was in, our group of evil adventurers was hired a local count to clear an old abandoned monestary of monsters. We did the job and got double crossed. (We were all rather evil, but tended to have enough of a code to keep our contracts.)
We ended up taking over his lands, getting official recognition from the king, and starting making that little burg the most prosperous county in the kingdom, one evil brick at a time.
The 'kingdom' only had two seaports, on either coast of the continent, and much of the middle was undefended and overrun by monsters with pockets of civilization here and there. It was /ripe/ for a bunch of power hungry evil bastards to take over and slowly mold to their own image. - We made use of every advantage that our lands, its neighbors, and its materials had to offer.
My personal favorite part of this, was the fact that my character personally corrupted the local goblins into a variant form of Pharasma worship. - All over our county, instead of raiding, goblins could be found doing /all/ of the most dangerous construction work, secure in the knowledge that when they died (and boy, the casualty rates in goblin engineering are astronomical) would live forever immortalized in the work that they were doing.
It kept the goblins busy, kept the population down as they would die by the thousands trying to erect bridges, mine materials, quarry stone, build roads, etc. All we had to do in reconompense was make sure each little monument of engineering had a plaque on it somewhere saying "Stinkpits died putting up this pylon." - It was beautiful.
Anyway, I digress a bit. The point is that sometime the logistics are part of the fun and part of the challenge.
As no one else has mentioned it yet, I feel I should bring up the city of Ipeq in Osirion.
Legend states that Ipeq was created by the legendary Pharaoh of Blades in a single day as the culmination of multiple wish spells provided by a conscripted army of noble djinn and efreet. It is said that one day the pharaoh's web of binding pacts will simultaneously expire and the genie host will suddenly return to sweep Ipeq away into nothingness.
@OS_Dirk, thank you for taking the time to describe some of the roleplay aspects of building cities. So much nicer than just mechanically working through the building pricelist.