First of all, awesome of you to experimenting with the gamemodes.
People may say otherwise however it allows for some good experimentation, which is the only real way you'll learn anything in level design.
Just a couple things I noticed:

You WILL be bitched at for this, if there's any major no-no in tf2 cosmetics it's flashing/coloured lights. In an alpha's scope it's pretty trivial, but just a head's up.

There's really no reason for this to be down there, water is in itself a "heath pickup," as it's a counter for pyros and it gives player an escape route to leave the battle. Also, it's really big, and the fog distance makes it hard too see in front of you
Either one of theses roofs (the one I'm standing on or the main one in front of me) needs to be risen or lowered, right now it's at a teasing crouch-jump distance yet is too high. Also your level's ceiling for this area is WAY too low, average out the height of a vertical rocket/sticky jump from your highest reachable ceiling and give it another 256 units.
OH GOD TRAPPED IN A TRANSFORMER SEND HELP
Also what Metalkev said about the flanking routes is right, it's pretty much just a labyrinth of hallways.
By all means though, throw it up for the next gameday or sit around in chat and see if anyone starts throwing the words "impromtu" around. I'd suggest at least giving a little more vertical room and taking out the flashing lights before you do.