Magic staves are an unusual item, because they are really a combination of multiple items.
Given that it is long (usually as long or longer than the owner is tall), requires two hands to use with any hope of success, and never has much in the way of useful blades or hooks or anything "weapony", all magical staves are simple two-handed weapons that share many of the qualities of a quarterstaff. In fact, any feats or abilities that apply to quarterstaves can also be applied to a mage's staff.
A mundane version of a mage's staff can be purchased at character creation for 80 gold.
Like a quarterstaff, a magic staff must be wielded in both hands in order to be considered 'wielded'. Like any other wielded magic item, magic staves provide no benefits unless they are being wielded. You cannot buy a staff, keep it in your backpack, and expect it to give you bonuses.
Unlike a common quarterstaff, however, a magic staff provides a number of benefits to its wielder, even before taking into account the magical abilities it grants.
First, when wielded, a magic staff can be used to make normal melee attacks against a creature within reach (using the stats of a mage's staff), or it can be used to perform Melee Touch Attacks against a creature within reach. If used to perform touch attacks, the magic staff's basic attributes are still the same, but the wielder may not apply their STR modifiers to their damage roll. This has a hidden benefit, though, if the wielder happens to have a negative STR modifier, it has no impact on the damage dealt.
Second, a magic staff counts as an implement, granting the wielder their Implement Bonus, if they get one, any time they must roll a to-hit roll when casting a spell or using a spell-like ability. As with other implements, magic staves can be used to perform a spell's somatic components, waving the staff around instead of the caster's bare hands. Furthermore, as long as the spell caster actually possesses the appropriate material component in a readily available location (like a Component Pouch), a magic staff eliminates any need to have a free hand to draw that component when casting the spell. The component is consumed as normal, but it is pulled from its storage space by the staff itself. If the component is stored in a location that would take longer than the "part of the same action as casting the spell" to draw, the staff cannot draw the component. Don't store your components in a portable hole, or back in town. It won't work.
Lastly, similar to a rod, a magic staff has charges that are consumed when spells are cast from the staff. Unlike a rod, all magic staves have a maximum of 15 charges available to them, and these charges automatically return at the end of each full night's rest (or 24 hours, whichever is sooner.) As a result, magic staves are always of some use every day. In addition, a magical staff can also be recharged with the use of a Large Manastone. Note that instead of a Small Manastone, staves require the purchase of a Large Manastone, so recharging them this way can be a bit expensive, no matter how useful it is.
Each time you cast the spell from the staff, you must make a Use Magic Device check to cast it, unless the spell is a spell that is present on your character class' class spell list. Even if you are too low level to cast the spell normally, or you haven't learned that spell, as long as you could learn it eventually from your class spell list, you can skip this check. Everyone else needs to make the check. The DC of the check is 5 + (2x creator level of the staff). If you succeed on the check, the spell is cast. If you fail the check by 4 or less (a normal failure), you waste the action required by the staff to cast the spell and nothing happens. If you roll a natural 1 or fail the check by 5 or more (a critical failure), you waste the action, no spell is cast, but a charge is used up on the staff.
Building A Magic Staff
Magic staves are composite items, that combine the functions of between two and four rods and/or wands. There are billions of possible combinations that can be 'built up' to make a unique staff for each individual player. To build a magic staff, simply select between one to three Magic Rods, and one to three Magic Wands. You must have at least one of each type of item in a Staff, and you cannot have more than a total of four. Add the cost of all your chosen items (at the caster level you want them to function at) together. You can make a Staff with:
- One rod and one wand.
- Two rods and one wand.
- Two rods and two wands.
- Three rods and one wand.
- One rod and two wands.
- One rod and three wands.
The sum of the costs all these parts is the cost of that magic staff. The staff is able to make use of every effect granted by all four items, as long as it is being wielded in both hands, and as long as it has charges remaining. Effectively, while wielding the magic staff, you are treated as wielding all of the selected rods and all of the chosen wands at the same time (and you gain the ability to make melee touch attacks, can apply your implement bonus, and can enchant the magestaff as a magic weapon on one or both ends if you would like).
Casting any of the spells from the chosen Magic Rod or Rods still requires a command word, uttered as a Standard Action, but instead of only using 1 charge per spell cast, the number of charges used is equal to the spell level of the spell. This means a 4th level spell (such as the Boneshatter spell from the Bonebreaker's Rod) uses up 4 of the staff's 15 charges for the day, but a 1st level spell (such as Magic Missile from the Rod of Darts) would use up only 1 charge. If a magic rod that casts a 0th level spell is chosen to be part of the magic staff's composition, it can be cast an unlimited number of times, since it costs 0 charges (though it still requires a normal action to cast).
The caster level of any spells cast from the magic staff are equal to the caster level of the rod or wand they are being pulled from. You can buy all of the rods and wands in a staff at different creator levels if you want to. That is, while you can purchase the Bonebreaker's Rod as a caster level 7 rod, the damage dealt by its Boneshatter spell is stuck at 7d6+7, and will not increase unless the staff is upgraded to make use of a higher level version of the Bonebreaker's Rod. This means that a magic staff that is able to cast three maximum level spells will be quite expensive indeed. This also means it is necessary to separately track the creator level of each rod and wand used in the staff's construction.
The wand effect or effects chosen for the staff does not use up any of the staff's charges, but they can only be used if the staff has at least 1 charge remaining.
Wand effects can be used to modify/alter the caster's own spells during their spellcasting, or they can be applied to the spells cast from the staff, but only if the caster meets the prerequisites normally required by the wand. (For example, to make use of the Wand of Quickening, the wielder must actually know the Quicken Spell feat. A staff imbued with the ability of a Wand of Quickening would have the same requirement of its wielder.)
You can upgrade an existing magic staff to have a higher caster level for one or more of the rods or wands imbued into the staff. The cost to do this is simply the difference in cost from the old rod or wand to the new rod or wand. This only apples to upgrades within the same rods or wand as are already imbued in the magic staff.
It is also possible to build a magic staff with fewer than four abilities (as noted above). If you wish to upgrade the staff later to add a rod or wand ability, as long as it does not push the magic staff above the maximum possible (i.e. four total abilities), you simply pay the cost of the new rod or wand being added to the staff.
It is only if you want to change out an existing ability of the magic staff (swapping out one rod or wand for a different one) that you must purchase a completely new staff.