The whole platform agenda can be easily viewed from the respective team's base, so those snipers could give you a nice little uncharged leg shot and knock you off. Also the platform pattern has a few choke points, where you have you to go, and some demo with extreme grenading skills could plant some pipes for your pleasure. All right, I think I put enough emphasis on that flag. Anyway, the base is quite challenging to defend as an engineer, Demoman aren't that practical, so you are left your classic pack of sexy HWs. The lack of any true sniper area makes an impact, because people have to think otherwise then snipe, and camp the snipers.
Offense is quick and dirty.
Pressing that button should not prove much of a challenge, just take the little vent backdoor and smash that use key wildly as 5 HWs open up fire. Just to note, you cannot press your own team's button. There is only one true entrance. The 2 vents, one leading to the button room, the other to the main base room, doesn't serve much of a stealthily purpose as must would think. One of most hated problems to mappers, aside from leaks, is when one brush is moved wrongly during compilation.