Inspired by people using the brickwork to interlock the corners of a laser cut building I had a go at drawing out my 'test shed' with the sides designed to interlock. As the material to hand was 3mm MDF (I have some 1.5mm and 1mm on order) I cut out the stretchers on the joint. This screenshot of TurboCAD shows what I mean.

The resultant kit of parts was amazingly fine and just demonstrates what the cutter can do.

The detail on the 'fingers' of each side shows the closure half brick and the header really well. This picture also shows up the engraved 'air bricks' just under the eaves. I'm almost tempted to try and put a row of tiny dots to represent the holes.

The completed building just slid together and I was amazed how it just fitted exactly into the base I had cut for it. Bear in mind that this photograph shows the parts just dry fitted together.

Mostly for my own reference later this was cut on our 60W laser cutter with the following settings

mortar cuts:- Cut with speed 60 and power 15%

engraving (for air bricks) speed 400 and power of 21%

cutting for walls etc: Cut with speed 35 and power 100%

I suspect that ultimately I'll find the better way to go is to use 1.5mm MDF and then interlock the headers and have a core of 3mm MDF with rebates in for windows etc.

Further to previous entry on putting a 45 degree mitre on the MDF I found I could actually do this more easily with a Dremel tool. The drill press I purchased some years ago is useless as such because it isn't really rigid enough however it works fine for this purpose. With a few bits of scrap to form a gate I was able to cut the angle quite accurately. (Please note the tool was rotating and cutting the material AWAY from the PC keyboard!)

Thanks everyone for your advice and encouragement.

David