1. Not usually. Most effects cap your caster level at your character level. A few let you go above it, but usually only for certain spells or groups of spells.
2. You are correct; you can't make wands/scrolls/potions, but you can make wondrous items &c.
As I understand it, a Scroll of Shield won't let you craft Bracers of Shielding without the +5 DC for not knowing shield because you need to have access to (i.e. "cast") the spell in question every day of crafting. If you're taking twelve days to make the Bracers of Shielding, you would need twelve Scrolls of Shield, one for each day of crafting.
I'm not sure where you're getting the caster level having a minimum of 3, though. Shield is a first-level spell; it has a minimum caster level of 1. So it would only take four days to make it and consume 2000gp of resources.
Of course, Bracers of Shielding would be a custom item, so it is also subject to GM approval. A +2 heavy shield would have a base price of more than 4000gp and use a hand slot and impose an armor check penalty and arcane spell failure chance, and would still only provide the same +4 shield bonus to AC; it seems like a custom Bracers of Shielding would be undercosted.
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I have just started playing pathfinder after nearly a 10 year break
from DnD. Have a few questions I could not find anywhere or had more then one answer.* 1. Can my caster level be higher then my charecter level.
* 2. How does crafting an item (wonderous, weapon, armor) if I do not have the spell on my spell list. This is from the book.
"Most of the time, they take the form of spells that must be known by the item's creator (although access through another magic item or spellcaster is allowed)." and "In addition, you cannot create potions, spell-trigger, or spell-completion magic items without meeting its prerequisites" I think that means I cant make wands, scrolls and potions but I can make weapons, armor, wonderous items, rings.I understand that my DC to craft it at the end increases for not knowing the spell.
Example: I want to craft bracers of shielding (continuous) but can not cast shielding though have a lvl 5 sorcerer.
Base Cost: Caster Level(min3)x Spell Lvl(1)x 2000x2(for duration)
=12000gold base cost. So will take 12days to make normally(in town).Can I make it using a Scroll of Shield.
1. Yes, but it is rare. Usually for a specific spell or subset of spells, such as granted by certain traits. There is, for instance, a carrion crown campaign trait that increases your caster level for one spell of your choice. It is up to debate whether that means you have a +1 caster level for the purpose of qualifying for feats and the like.
2. You can use the scroll to get around the +5 penalty you would otherwise have for not knowing scroll (AFAIK).
@Roberta Yang: Are you saying that the effect itself must say it is capped at your character level? I can think of traits that specifically do not state this.
You have a total of 30 caster levels, but you still only have a caster level of 17 in your arcane class and 13 in your divine class, both of which are less than your character level of 20. At no point are you considered "caster level thirty"; your caster level would be either 13 or 17 depending on the spell in question. Taking that third-party feat would just give you a caster level of 20 in both your casting classes.