I usually extractor trick to get 10/9 drones, and scout at 0:55, and then one more scout at 1:15 on 3 and 4 player maps to the other location(s). If I see a refinery building or finished, I generally prepare for some form of early vulture harassment by having a good wall. Usually putting a creep colony down by 3:30 and morphing it into a sunken immediately after is enough to prepare for this first vulture. There is one super quick vulture rush out there like 8/10 Barracks, 8/10 Refinery, 10/10 Factory at 2:00, 10/10 supply depot, but you will know if they are doing this if you pay close attention when you scout them because the supply depot will come VERY late. If they do this build the vulture can actually arrive at your natural by 3:30 or earlier if they proxy the factory. Anyway...
I have included walling ideas for the following maps: Autobahn, Benzene, Cross Game, Destination, Heartbreak Ridge, Match Point, Overwatch, Polaris Rhapsody, Third World, Aztec, Loginus II, Medusa, Tau Cross, Circuit Breakers, Colosseum, Fighting Spirit, Gladiator, Ground Zero, In The Way of an Eddy, and Jade.
If you see a creep colony it is just there to help you with positioning, so don't build it.
I will finish Roadkill, Neo Sylphid, Labyrinth, and Transistor later this week. If there are other maps I should do please let me know.
Some of the issues with walling: the wall messes up drones gathering gas/minerals. The wall is too tight, so that a drone can't get out to go expand to your third base. If you 12 hatch and want to place a creep colony at 3:30, you might not have enough creep spread by then, which will delay your defense. The hatchery is placed in a position that traps ultras from getting out once the sunken is removed (mainly bottom left position in Circuit Breaker). I tried to make walls that don't break these rules, unless I have written otherwise on the picture.
The ways I have presented are by no means the only solutions, there is some leeway in the exact placement of some solutions, but I have generally chosen a way that helps the sunken protect the hatchery and hydralisk den from being too exposed to the vulture's shots.
Some maps and positions kinda suck for walling as Zerg like Third World (Top Position), Destination, Medusa (Bottom Left/Middle Right), Cross Game, COLOSSEUM!
If I have made any mistakes, or you think you have a better walling idea for some position on one of the maps, please let me know.