I want to point out that I do like the theme of a subterranean base that you've got going. I also think that the rooms are big enough and the flag room is big enough for sentry ambushes

The rooms might be too easy for demos to take out sentries. hidden around the corners. Perhaps make a small hallway leading to the flag rooms.
If at all possible I'd like to look over a canyon.... if not seal off the entire 'outside' area and make it an interior overlooking lava

The edge is nice, and you need a few broken hand railings here and there

Pyros will have fun blowing people to their doom.
The underground tunnel let's call it, there are a few spaces for spies to hide, but I'd like more spy nooks. Its too easy to just shoot straight ahead and have the possibility of shooting a cloaked spy. Perhaps extend the scaffold from the spawn area over and through or too the wall with some windows.
I think that you need to draw more focus on the doors leading to the interior. They are kind of shadowed. Signs, lights, maybe a little spot light on the doors just to draw attention
There should be some sniper points in the outside. Sniper points that are off the ground on a balcony through windows. You can still use the dump trucks for cover of course. Right now I foresee the snipers just standing on the ground and sniping through the dump trucks like its a Minecraft trade server.
I don't think your ceilings match up to the tops of your walls.
Hopefully this is constructive criticism and I'd like to see you continue it, because this isn't just a box map like everyone else's first map. Keep going. You'll get there
