help requested with cutting objects.

Hi, 

I'm an architecture student trying to make my design in grasshopper. I'm glad to say I can create the overal form of the design but now I want to try to create the floors, walls and openings and this is where I start losing myself in grasshopper. 

(this is the form i want, tho the design of the openings is still not finished)

When I try to create a floor: I extrude a plane with the thickness I want and then I want to cut it with the form I created in grasshopper but it says it can't do that.. Tho cutting with a plane works fine, but then my floors will lack the curved edge if I just extrude them.

I was thinking of creating the openings in a similar way, but first I need to solve why it doesn't cut. I think the problem lies with the loft as an open brep and the extruded plane as a closed one.. But i'm fairly new with grasshopper and don't know how to solve this..

Is any1 willing to help me get on my way?