That's not much information :-)
What point-buy, which books, what do you want to achieve, which level do you start?
If you go for intimidate, I strongly recommend going for shatter defenses. Add enforcer, sap master and skill focus intimidate - and you will leave your foes with so many penalties and make you able to sneak attack that you will be very dangerous :-)
Definitely grab a dice set and roll those stats, 5d6 drop 2 is MUCH better than 25 point buy.
the forums will roll for you... put "dice" in the [ ]s then what dice (it won't recognize 5d6 drop the two lowest, but you could put 1d6 in 5 times and add the best 3) and end with "/dice" in the [ ]s
edit: so that would be a 14 (there's maybe a clearer example in the "how to format your text" section below)
actually, that was more fun than it should be- lol
here's the other 5
there you go- 10, 17, 13, 12, 15; plus that 14 (equivalent to a 30 pt buy)
Yeah, definitly do the 5d6. I rolled a 4d6 chracter once, and I have 3 stats at +3. Which is nice. Otherwise, what d you want to do with your ninja? Kill people? Trick people? That will change how you want to build. I like tricking people myself.
Ooh, if you want DPR, rogue/ninja might not be the best class for you. Really not. You might want to go zen archer (who can flurry with their bow, shooting out twice as many arrows as everyone else at no extra cost), or two handed fighter (because you add 1.5 times strength to each hit instead of 1). Rogues can do a decent amount of damage, but they're very situational, because you're so fragile, and you rely on flanking/sneaking to be able to deal any damage at all.
If you want to maximize DPR, find someone in the team to be your flanking buddy, this should let you set up sneak attacks more easily. Look into some of the guides.
However, there is no "nova" systems. In pathfinder, rogues are seriously underpowered, and get few to no options to "assassinate" creatures (and all the most powerful creatures are immune (or nearly so) to such effects). Rogues are glass cannons, not a DPR class. With luck, they can dish out a single powerful hit, bu it's hard to do consistently.
Note: Because of the whole 5d6 case, you will be highly advantaged as you can probably roll up some decent numbers for several stats. This can allows you to play MAD (multiple ability dependent) classes like the ninja.
Note 2: Also, rely on you team mates. You're all in this together. Don't play this like a video game, because you will be sorely disappointed.
oh- in that case... 3 levels of two handed fighter, 1 level dip in ragechemist/vivisectionist alchemist, and the rest in barbarian! take EWP[Tetsubo] and power attack. (tetsubo is 1d10 with a x4 crit.) start with 20 Str- with mutagen and rage you'll be at 30... enlarge person and bull's strength would put you at 36 str at like 5th or 6th level! talk one of the veterans into a 2wpn fighter with kukris and the butterfly sting feat. he'll threaten on 18-20 (15-20 once keen or Imp. Crit) and allow you to take the crit... your 36 str = +26 dmg; +6 from power attack- with only those 2 bonuses your crit would do 8d8+128 (1d10 goes to 2d8 with enlarge) at 5th or 6th!
edit: i like the forum dice roller, so here example damage
EWP= Exotic Weapon Proficiency, yes
truthfully, there is no bad order to take those classes in... alchemist at 1st wouldn't be great but other than that, however you like. barb 1 will score you 2 extra hp (since you get max at 1st) and let you rage in a pinch right away... that may be the best. at 24 str (when raging) the benefit from overhand chop is better damage than the boost from mutagen, so i guess your best bet is:
1- barb 1
2- fighter 1
3- fighter 2
4- fighter 3
5- alchemist 1
6+- barb 2+
that's an oversimplification, though. at some point you might want to add another level or two of fighter for weapon spec. and weapon training. and, another level of alchemist gets you a discovery (i especially like preserved organs), and opens up the extra discovery feat, 2 would also get you another 1d6 of sneak attack (and each level adds 10 min to mutagens duration). but i'd take at least a couple barb levels in the 6-10 range, just to make sure you have enough rounds of rage.
I would tend to agree with nate. From what I've heard, a raging barbarian pretty much has the highest DPS.
I'm making a tengu rogue, and I plan on dual-wielding wakazashi (1d6 18-20/2 exotic light weapons) and using Butterfly Sting to help the greataxe-wielding tank. :-)