The cabin on our land is a lot like what you are describing. When we first bought the land for our retreat it had a partially finished 2 room concrete block building with a foundation, doors and windows, but no roof. When you walked in the door you could look up at the sky.
Our first major project was to roof the cabin. I decided on a simple gable rafter roof so we could have living space on the second floor. First I used a hammer drill to make holes for the sill bolts. Used 1/2 inch redheads. After mounting 2X8 on top of the blocks I build the second floor; first laying joists, then 1/2 plywood. After the floor was complete I prepared a 24 foot long ridgepole by splicing two 2X12's with plywood. Once the ridgepole was propped 9 feet above the second floor, I started cutting the rafters with a 9 over 12 slope. Plywood over the rafters, then felt, then metal sheathing. The whole project took a whole summer of weekends.
In your case, plan ahead as to where you will want openings and fixtures. Imbed bolts and places to insert screws before you start finishing. I would not put insulation in the blocks. If you want a really strong block structure, fill the blocks with rebar and concrete. Then insulate the outsides of the blocks.
In my case I am anchoring 2X4's with a nail gun to the walls, then laying foam insulation. This will be covered with standard sheetrock. Around the woodstoves, I replaced the sheetrock with cement board. It was a pain to work with, but now the perimeter of my stoves are totally non-flammable.
Later, if I want, I can do a second layer of insulation on the outside walls of the cabin. I'll powder nail 2X4's again and lay insulation, but will cover it with metal sheathing instead of sheetrock.
Good luck to you,
Michael
