From the SRD:
SRD:Staff of the Magi
A long wooden staff, shod in iron and inscribed with sigils and runes of all types, this potent artifact contains many spell powers and other functions. Some of its powers drain charges, while others don’t. The following powers do not drain charges:
detect magic
enlarge
hold portal
light
mage armor
mage hand
The following powers drain 1 charge per usage:
dispel magic
fireball (10d6 points of damage, DC 13)
ice storm
invisibility
knock
lightning bolt (10d6 points of damage, DC 13)
passwall
pyrotechnics
wall of fire
web
These powers drain 2 charges per usage:
monster summoning IX
plane shift
telekinesis (400 pounds maximum weight)
whirlwind
The staff of the magi gives the wielder spell resistance 23. If this is willingly lowered, however, the staff can also be used to absorb arcane spell energy directed at its wielder exactly like a rod of absorption. The staff uses spell levels as charges, not as spell energy usable by a spellcaster. If the staff absorbs spell levels beyond its charge limit (50), it explodes as if a retributive strike had been made (see below). Note that the wielder has no idea how many spell levels are cast at him or her, for the staff does not communicate this knowledge as a rod of absorption does. Absorbing spells is risky, but absorption is the only way this staff can be recharged.
Retributive Strike: A staff of the magi can be broken for a retributive strike. Such an act must be purposeful and declared by the wielder. All charges in the staff are released in a 30-foot spread. All within 10 feet of the broken staff take hit points of damage equal to 8 times the number of charges in the staff, those between 11 feet and 20 feet away take points equal to 6 times the number of charges, and those 21 feet to 30 feet distant take 4 times the number of charges. Successful Reflex saving throws (DC 17) reduce damage by half.
The character breaking the staff has a 50% chance (a 01-50 result on d%) of traveling to another plane of existence, but if the character does not (51-100), the explosive release of spell energy destroys her. Only specific items, including the staff of the magi and the staff of power, are capable of a retributive strike.
Caster Level: 20th; Weight: 5 lb.
I can work this up using the spell slot item creation system from the Artificer's Handbook, but I can tell you before I even put down the first number that A) a single wizard probably could not create such an item and B) it's going to cost a fortune. But let's proceed.
Essentially, the staff has the following powers, all operating at caster level 20.:
detect magic, enlarge, hold portal, light, mage armor, and mage hand all castable freely, an unlimited number of times.
dispel magic, fireball, ice storm, invisibility, knock, lightning bolt, passwall, pyrotechnics, wall of fire, and web all consume 1 charge from a common charge pool. Lightning bolt and fireball have a reduced DC (why, I know not).
monster summoning IX, plane shift, telekinesis (400 pounds maximum weight) - caster level 16, whirlwind
It also grants spell resistance 23, which you want to exclude. Then there's a whole bunch of stuff about exploding, and absorption which I'll tackle later.
First, the free spells:
detect magic (0) (1 min per/lvl) 3 spell trigger use-per +15 1 min per level
enlarge (1) (1 min per/lvl) 3 spell trigger use-per +15 1 min per level, +1 for second effect
hold portal (1) (1 min per/lvl) 3 spell trigger use-per +15 1 min per level, +2 for third effect
light (0) (10 mins per/lvl) 3 spell trigger use-per +13 10 mins per level, +3 for fourth effect
mage armor (1) (1 hr per/lvl) 3 spell trigger use-per +15 1 min per level, +4 for fifth effect
mage hand (0) (concentration) 3 spell trigger use-per, +5 (permanent), +5 for sixth effect
The cost for each effect is spell-trigger based, use-per (unlimited uses), and has a cost based on the spells duration (most of them are +15 for the 1 minute per level spells, but light is 10 mins per level, so has a decreased cost) - it costs less to cast a longer duration spell. Mage hand is a special cost, since our rules don't cover costs for spells with a duration of "concentration", I ruled that it's essentially permanent, which is the cheapest cost for this type of effect. The numbers 3, +15, etc., are the number of spell slots required. A wizard would need to have a total number of spell slots available to cast this many 1st or 0 level spells. Let's figure up the totals:
(1st level) 3+15+1 + 3+15+2 + 3+15+4 = 61
(0 level) 3+15 + 3+13+3 + 3+5+5 = 47
A wizard (or sorcerer) would need to be able to cast 61 first level spells, and 47 0 level spells in order to create just this part of the item. A 20th level sorcerer has spells per day of 6/ 6/6/6/ 6/6/6/ 6/6/6 and if he has a 30 Charisma, he's getting bonus spells of 3/3/2/ 2/2/2/ 1/1/1. Because he can use 2nd, 3rd, etc. spell slots to cast 0 and 1st level spells, let's see if he can actually cast a cantrip 47 times. 6 (0) + 9 (1) + 9 (2) + 8 (3) + 8 (4) +8 (5) = 48. He could cast 48 0 level spells by exhausting all of his 0, 1st, 2nd, 3rd, 4th, and 5th level spell slots. That would give him an item that could freely cast, with unlimited uses, light, mage hand, and detect magic.
Let's exhaust the rest of his spells and see how far he gets.
1 (5th, left over) + 8 (6) + 7 (7) + 7 (8) + 7 (9) = 30 first level spell slots. That would be enough to give him the Enlarge effect (19 total spell slots (3+15+1), which would leave him with 11 spell slots.
As you can see, a 20th level sorcerer, with a 30 charisma would be unable to make such an item in the tradition sense. In reality, he would have to make it slowly over time. Adding magic to it over a long period of time. This would actually increase the cost, because adding magic to an existing magic item costs more than just making it all at once. Otherwise, he'd need a ton of help.
Let's examine the cost of this portion of the item (assuming that the sorcerer is actually able to create just this portion of the item).
(1st level) 3+15+1 + 3+15+2 + 3+15+4 = 61
(0 level) 3+15 + 3+13+3 + 3+5+5 = 47
The formula is expressed as 10gp (spell level + caster level -1) * (# of spell slots) ^2
working through each spell we get (using a caster level of 20):
10(1+20-1)*(19)^2 +
10(1+20-1)*(20)^2 +
10(1+20-1)*(22)^2 +
10(0+20-1)*(18)^2 +
10(0+20-1)*(19)^2 +
10(0+20-1)*(13)^2 =
200*361 + 200*400 + 200*484 + 190*324 + 190*361 + 190*169 = 72,200 + 80,000 + 96,800 + 61,560 + 68,590 + 32,110 = a creation cost of 411,260gp
So, a 20th level sorcerer with a 30 charisma would be 31 spell slots shy of being able to create just this portion of the item, and it would cost him 411,260gp. Even if he had a 44 charisma, he'd still be 15 spell slots short.
Now, if you're playing in some kind of uber munchkin game, and you insist on knowing how to create the rest of it, I can go through that, but it's obvious to me that this item is most definitely an artifact, and shouldn't be created through normal means.