I can't, it just says "float".

I have a colorset which has an invisible color. For you, put down the brick, and then take out the wrench, and on the bottom of the menu.
Theres three options
[√] Ray Casting
[√] Collision
[√] Rendering
Uncheck Rendering, and it'l go invisible, uncheck Collision, and you can walk through it, uncheck Ray Casting, cars can go through, camera, bullets, and you can't click it.
So uncheck Rendering, and then build the plates ontop of that, leveled with the wall.