Please, for the sake of all your players, make these nonsolid. I don't want to hit my head while jumping, get caught on it, or die by the hands of my opponents.
These support look awkward and are awfully thin. I try to keep my crossbeams as well as the columns at the same thickness. If they're used in a hallway (as in the path to A), clip in when it's against the wall. There's some small collision issues and places to get caught everywhere.
I know you clipped your stairs, but there's still small jittery bumps everywhere! Either clip the edge of the platforms or raise the displacement. If you choose the former, I'd use blockbullets.
Keep your stairs/ramps mostly consistent please! 1:1 works in rare clases, but most mappers use either 1:2 or 2:3 for stairs. More of a nitpick and your steepness is fine, but consistency is nice.
The ceiling looks odd, but that's mostly me.
In chat the other day, you didn't know how to optimise with all the angled roofs. It can be tricky. Since it's alpha, focus more on gameplay. Flat roofs might be easier for you to work with for the time being.
Some areas might need a raised skybox for jumping classes.