Here the examples.
I hope they help other people to set something like this up, after mifki did the changes he just described. Both sprites are taken from Warcraft II: Orcs vs. Humans, by Blizzard. Copyright & TM.
Add to entity:
[PERMITTED_BUILDING:BLACK_ALTAR_ORC]
[PERMITTED_BUILDING:TINKERER_ORCISH]
Add to any building file:
[BUILDING_WORKSHOP:BLACK_ALTAR_ORC]
[NAME:Black Altar]
[NAME_COLOR:7:0:1]
[BUILD_KEY:CUSTOM_SHIFT_X]
[DIM:4:4]
[WORK_LOCATION:2:2]
[BLOCK:1:0:0:0:0]
[BLOCK:2:0:0:0:0]
[BLOCK:3:0:0:0:0]
[BLOCK:4:0:0:0:0]
[TILE:0:1:11:12:32:32]
[TILE:0:2:27:28:32:32]
[TILE:0:3:32:32:32:32]
[TILE:0:4:32:32:32:32]
[COLOR:0:1:7:0:1:7:0:1:0:0:0:0:0:0]
[COLOR:0:2:7:0:1:7:0:1:0:0:0:0:0:0]
[COLOR:0:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:0:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:1:1:32:32:32:32]
[TILE:1:2:32:32:32:32]
[TILE:1:3:32:32:32:32]
[TILE:1:4:32:32:32:32]
[COLOR:1:1:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:2:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:2:1:32:32:32:32]
[TILE:2:2:32:32:32:32]
[TILE:2:3:32:32:32:32]
[TILE:2:4:32:32:32:32]
[COLOR:2:1:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:2:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:3:1:0:1:2:3]
[TILE:3:2:4:5:6:7]
[TILE:3:3:8:9:10:11]
[TILE:3:4:12:13:14:15]
[COLOR:3:1:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:2:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:3:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:4:7:0:1:7:0:1:7:0:1:7:0:1]
[BUILDING_WORKSHOP:TINKERER_ORCISH]
[NAME:Orcish Tinkerer]
[NAME_COLOR:7:0:1]
[BUILD_KEY:CUSTOM_SHIFT_Y]
[DIM:4:4]
[WORK_LOCATION:2:2]
[BLOCK:1:0:0:0:0]
[BLOCK:2:0:0:0:0]
[BLOCK:3:0:0:0:0]
[BLOCK:4:0:0:0:0]
[TILE:0:1:11:12:32:32]
[TILE:0:2:27:28:32:32]
[TILE:0:3:32:32:32:32]
[TILE:0:4:32:32:32:32]
[COLOR:0:1:7:0:1:7:0:1:0:0:0:0:0:0]
[COLOR:0:2:7:0:1:7:0:1:0:0:0:0:0:0]
[COLOR:0:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:0:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:1:1:32:32:32:32]
[TILE:1:2:32:32:32:32]
[TILE:1:3:32:32:32:32]
[TILE:1:4:32:32:32:32]
[COLOR:1:1:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:2:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:1:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:2:1:32:32:32:32]
[TILE:2:2:32:32:32:32]
[TILE:2:3:32:32:32:32]
[TILE:2:4:32:32:32:32]
[COLOR:2:1:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:2:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:3:0:0:0:0:0:0:0:0:0:0:0:0]
[COLOR:2:4:0:0:0:0:0:0:0:0:0:0:0:0]
[TILE:3:1:16:17:18:19]
[TILE:3:2:20:21:22:23]
[TILE:3:3:24:25:26:27]
[TILE:3:4:28:29:30:31]
[COLOR:3:1:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:2:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:3:7:0:1:7:0:1:7:0:1:7:0:1]
[COLOR:3:4:7:0:1:7:0:1:7:0:1:7:0:1]
The tileset, in my case the name is "MDF 24x - Overrides Buildings.png"
The entries in the overrides.txt. Mind that the "5" means that this is my fifth tileset in use. The number on your machine might very well differ.
[TILESET:MDF 24x - Overrides Buildings.png:MDF 24x - Overrides Buildings.png]
[OVERRIDE:0:B:BLACK_ALTAR_ORC:Workshop::5:0]
[OVERRIDE:1:B:BLACK_ALTAR_ORC:Workshop::5:1]
[OVERRIDE:2:B:BLACK_ALTAR_ORC:Workshop::5:2]
[OVERRIDE:3:B:BLACK_ALTAR_ORC:Workshop::5:3]
[OVERRIDE:4:B:BLACK_ALTAR_ORC:Workshop::5:16]
[OVERRIDE:5:B:BLACK_ALTAR_ORC:Workshop::5:17]
[OVERRIDE:6:B:BLACK_ALTAR_ORC:Workshop::5:18]
[OVERRIDE:7:B:BLACK_ALTAR_ORC:Workshop::5:19]
[OVERRIDE:8:B:BLACK_ALTAR_ORC:Workshop::5:32]
[OVERRIDE:9:B:BLACK_ALTAR_ORC:Workshop::5:33]
[OVERRIDE:10:B:BLACK_ALTAR_ORC:Workshop::5:34]
[OVERRIDE:11:B:BLACK_ALTAR_ORC:Workshop::5:35]
[OVERRIDE:12:B:BLACK_ALTAR_ORC:Workshop::5:48]
[OVERRIDE:13:B:BLACK_ALTAR_ORC:Workshop::5:49]
[OVERRIDE:14:B:BLACK_ALTAR_ORC:Workshop::5:50]
[OVERRIDE:15:B:BLACK_ALTAR_ORC:Workshop::5:51]
[OVERRIDE:16:B:TINKERER_ORCISH:Workshop::5:4]
[OVERRIDE:17:B:TINKERER_ORCISH:Workshop::5:5]
[OVERRIDE:18:B:TINKERER_ORCISH:Workshop::5:6]
[OVERRIDE:19:B:TINKERER_ORCISH:Workshop::5:7]
[OVERRIDE:20:B:TINKERER_ORCISH:Workshop::5:20]
[OVERRIDE:21:B:TINKERER_ORCISH:Workshop::5:21]
[OVERRIDE:22:B:TINKERER_ORCISH:Workshop::5:22]
[OVERRIDE:23:B:TINKERER_ORCISH:Workshop::5:23]
[OVERRIDE:24:B:TINKERER_ORCISH:Workshop::5:36]
[OVERRIDE:25:B:TINKERER_ORCISH:Workshop::5:37]
[OVERRIDE:26:B:TINKERER_ORCISH:Workshop::5:38]
[OVERRIDE:27:B:TINKERER_ORCISH:Workshop::5:39]
[OVERRIDE:28:B:TINKERER_ORCISH:Workshop::5:52]
[OVERRIDE:29:B:TINKERER_ORCISH:Workshop::5:53]
[OVERRIDE:30:B:TINKERER_ORCISH:Workshop::5:54]
[OVERRIDE:31:B:TINKERER_ORCISH:Workshop::5:55]
Note that the tiles are unique on both workshops, the tinkerer shares no tiles with the altar, otherwise it would get mixed up, as mifki described. Its not important anymore I guess, when he finishes the custom_id system.
The end result, ingame screenshot:
You can easily change the black background to fit the grass, or constructed floor. This is just a quick example.