This list was taken (not stolen) from a post
made by spinnie on GTAForums.com.

Garage ID - Description
1 - Placeholder, DummyID. (doesn't do anything,
    initial garages get 1, and change type when
    a certain asset is bought)
3 - BombShop (8ball)
5 - Pay and Spray
7 - Car Eater, haven't got a clue what this is
    suppose to be, not sunshine autos anyways...
8 - Sunshines Autos Carshop, List 1
9 - Sunshines Autos Carshop, List 2
10 - Sunshines Autos Carshop, List 3
13 - DO NOT USE, CORRUPTS SAVEGAMES!
16..18 - In use Saving Garages
19 - Garage where you beat the cops up during
     "Copland"
22 - Sunshines Autos Carshop, List 4
23 - Garage to park the tank in during "Sir, Yes
     Sir!"
24..31 - In use Saving Garages
32 - Unused Saving Garage

