Cutting to the chase, the 'simplification' I had in directly attaching sloping roof to the flat roof does not work. The angles are all off and the 'step' section is needed as a kid of fudge to make everything connect.
There are two options - fill the side panels will cardboard as (for once an asset) the warpiness of the material it has a bit of give and could be bent to fit.
Alternatively, option 2: build it properly.
Either way, for the moment, this places the body on a back-burner. Thoughts instead turn to the legs...
The problem with the legs, for me, is expense. I don't have an infinite budget, so options are limited. At some point I may go back on fill in my thought processes, but for the moment every minute I spend typing this, is one minute less on the actual build. I'll skip to the end, therefore, and tell you what I decided upon.
450mm square, 1500mm long fence posts. Annoyingly, the stock control at my local Homebase is awful, which meant I had to travel. I could have gotten more wood for less money, but it had to fit in the car and thus I ended up with what I did.
In more positive words about Homebase, a few years ago my local one moved (about 200m). During the clearout of the old store they left a pile of wood outside with a nice 'free' label on it. I've had a bunch of MDF sitting about in the shed ever since.
I've decided to attach the legs as you would a table, resulting in...
It's getting a bit tall now. It's also not super-stable, which may have to be dealt with later on. Hopefully (there's rather a lot of that going on with this build), once the feet are on, things will be improved in the not-toppling-over department.
Head attachment is problematic. Despite being cardboard, it's still a bit on the heavy side. Still having a length of MDF left after the leg-attachment, for the time-being, I've simply screwed that down to the base and, after cutting a slot at the front and back, slid the head on.