You would need everything it doesn't have A/C wise... compressor, lines, condenser, condenser fan, receiver/drier, etc. Could get spendy quick.
Look for leaks, check all the fluids, jack it up in the air and check the suspension, make sure everything functions, get it scanned and make sure there are no codes (OBDII), no check engine light, drive it hard, make sure it doesn't bog, have a funny idle, tranny shifts smooth. Look for quality in any extra wiring that was done, if anything looks out of place, bring it up.
PS - I got Jesus.