Since this topic is about doors the best hight ive found is 96 units, and 128 is good for a room hight as it lets u get a full jump.
Also if u can try build everything with the caulk texture. then paint/texture the parts of ur map,buildings that will show in game with crtl+shift.(selects 1 side of ur brush) That way… any hidden things that cant be seen dont draw in game helping the game to run faster.
Say u build a floor… only the top of ur floor will be seen in game. So u build ur floor with caulk texture then ctrl+shift and press the top of ur floor. and select ur floor texture. Now u should have a floor with 5 sides being caulk and the side u see being ur floor texture. In game this meens ur card will only draw the side u can see and dosnt draw the other 5.
I just build everything with the caulk then paint it once i feal i have finished it.
Also another thing that might help is. say u want to place a building onto ur open map.save ur map. Take a brush and make it the size of the bulding u want. then copy it. now open a new map and import the copyed brush. Now u have a floor plan for ur building :D. Just build away useing the floorplan as a reminder then once u have finished u can save it. then import the building into ur main map and move it into place :D.