Its quite simple ans I am with ctbram, there are so many ways to do this. I would however build the walls etc first, then you are left with the door opening cutouts. I wouls then select 3 faces in the cutout, there is no door frame on a floor. Then duplicate these faces, then use extrudes to create you door frame and door.
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes