Different disclosure laws apply to residential property with more than 4 units. If 4 or less, then the disclosures are more stringent. (look to California Civil Code section 1102 et seq p. 63+
http://www.dre.ca.gov/relaw.htm )
In any event....
1) get copies of all leases
2) get the property owner to give you a schedule e - if they have one or least a spread sheet of the schedule of rents and operating costs
3) if the owner had enlisted the services of a property management company - get that file for at least three years.
4) (**u are not required to do this, but you do, you have to disclose any material problems you find) look to see if the building is currently in violation of relevant zoning ordinances
5) (**u are not required to do this, but you do, you have to disclose any material problems you find) look for liens
6) find out any material defects with the property.
7) any easements or encumbrances otherwise?
8) all items required in the TDS that the city or county may require.