If it's anything other than 8, water glitches.
Darn... well, i'll just have to see what i can do then
Edit: I set the Square Size to 8, i got the terrain JUST how i liked it and as close as i could get it to how it looked on Garry's Mod, the water was fine too

But just as i restart and load the level back up, i realize, MY TERRAIN IS FLAT! I go looking for where the terrain sank in for the water, i find it outside my interior, it wasn't like that when i saved it, and even though the terrain moves from having it's Square Size raised, i made sure to flatten what terrain i already had and redo that part all over, i hadn't touched the Square Size at all afterward, so how did this happen, i could try to get my map back the way i want it just by moving the interior and water to where the edited terrain is, but i'm just so annoyed and curious as to why this happened...
Edit: Also, you can place bricks on all the stairs just fine, same with the white room, except plates, they can't be placed in the white room, the hallway outside the white room, nor every two stairs, but it's either i can't place plates, or i can't place bricks, either way, i can't place something in certain areas and there's nothing i can do about it unless someone has an idea