Abandoned Shack Floor

[Diamask]

I'm modding the Abandoned Shack near the Yangtze Memorial to be a player home, and I want to make a second floor for it. I was hoping someone with a little more Fallout modding know-how than I could chop a couple squares out of the floor for me. To illustrate:

 

http://img97.imageshack.us/img97/4526/bunker.jpg

 

I guess it's a fuselage, not a bunker. Anyways, in the GECK, the door is there on the right when you press 'T' for the RamshackleFuselageInterior01 model, to center over the top. I want that floor section above it, highlighted in red, chopped out so I can put some stairs in to the bottom. Maybe a but more next to it, to the left, if that's not enough space for someone to walk through.

 

Thanks.