ok, well duplicate the the cube, then select the outer cylinder then boolean the cylinder so ur left witha hole, do the same with the inner cylinder, then combine them both, then select the edges of the hole on the outer cylinder, then extrude them inwards, then snap the verts to the same places as the inner cylinder, then merge them. (sorry duplicate the cube 3 times) then change the thickness of the third cube so its door thickness then u got it. make some hindges and its all done (if u get what i mean , if not ill make it in maya and duplicate it every step so u can look at all the stages)

Matt