An update on my progress:
I settled on a minor variation of the 8x6, walk-in design I posted above. I realised I'd have to go into the run to open & close the 2 small windows on the end wall so I swapped them with the large window on the back wall. I also spent a good while in Google Sketchup moving things around until I was happy with position of windows, doors etc and until it looked "right". Next I drew up the framework in Sketchup to use as a guide when it came to the actual building. Again I spent a lot of time in Sketchup figuring out the best way to constuct the frame as 4 separate walls, and how the roof would be supported etc.
The frame plan: 6' x 8' floor area. 7' high at the front, 6' high at the rear. Rafters for the roof (not drawn) will run front to back with a 1 foot overhang on all sides.
The floor: the site was cleared and concrete blocks bedded into concrete at the 4 corners. The 5x2 floor frame rests on the 4 corners. The red bricks are mainly there to prevent anything making a home underneath (mice, rats etc) but since they're also bedded in concrete they'll help to support the structure too.
The finished frame: (it was nearly dark by the time we finished). The finished frame probably runs about 95% to plan with some minor changes made as we went along.
The siding in progress: the outer walls are lapped 7x1s. Inside will be insulated and lined with plywood or possibly corrugated plastic. The siding is quick to install but takes alot of thought before each cut to ensure I'm making best use of the raw materials. Note in this photo I've forgotten about the pop door, which SHOULD be at the right hand end of the short wall.
More photos to follow as the build progresses.
Peter