An interesting concept, but I think it might be too easy for the attackers (especially with the ice on the boxes). You should make sure you can't touch the base as the defenders (you can die at the window by the capture point). I would also look into using some different textures. Try to make it look more like a real setting - maybe a school building or something. Wood planks with holes cut out just doesn't look very immersive.
I've put the map up on the beta server so you can play test it. See PM for details.
