Honestly, I wouldn't start with the "lesser" races.
The Savage Species (
SS) concept of the monster (racial) class is in many ways a better fit...especially if you do it the way Monte Cook did it in his Arcana Unearthed/Arcana Evolved (
AU/AE) setting.
Essentially, you pare down the race to a one that would be balanced for a +0LA race, then break up the remaining benefits that race gains that would normally give it a LA over several "racial" levels. These racial levels don't count towards favored class penalties, but DO count as PC levels.
In the original SS form, the PC would have to take all of those levels first before taking any class levels. And in addition, those levels didn't necessarily grant everything a normal class level might, like HD.
In AU/AE, the levels are fully fleshed-out levels with HD and all at each level. However, a PC 1) need not take any levels in that "Racial class" before taking a character class, 2) need not take them all at the same time, and 3) need not take them
at all- just like a regular character class. Use the
MM list of types and subtypes to determine HD type, BAB & save progressions, weapon & armor proficiencies, etc. for their racial levels.
(While not a rigid rule, I personally design 1 racial level per +LA.)
Once I designed a standard +2LA racial class for the more common Githzerai race, then and only then would I bother considering Githzerai from other sources that might be lesser or greater than what we see in the
MM or XPH.
In the case of the standard Githzerai, I'd give them:
1) a +2Dex -2Int and +1 Wis adjustment, +1PP, Darkvision, Power Resistance = HD +3*, their automatic & bonus languages, PLAs 1/day Inertial armor, Psionic daze, Catfall, Concussion Blast (Manifester level 1/2 HD -2, minimum 1st*), and Favored Class: Monk at the base (+0LA) racial level,
2) +2Dex at the 1st racial level, +1 PP, +1 use/day of the PLAs, and
3) +2Dex and +1 Wis, +1 use/day of the PLAs, and add PLA plane shift 1/day when PC is 11th level at the 2nd racial level.
* This was lowered because by virtue of these racial class levels, a Githzerai will have +2HD that they normally wouldn't have.