Thanks for all the help & advice guys!
a) I can't close in the existing carport at all (council regs), and anyway Boxhead is right - not enough room to open the car doors.
b) I actually, begrudgingly, am rather fond of Kevin, so can't put out a contract on him
c) A wider roller door is probably the best idea. I have, however, a supporting post in the middle which I would have to move - structural challenge (but not impossible). I've decided therefore to actually go for the 2.5m door and probably employ GoJacks. Then I'll review things in a few years when the car is built - perhaps getting a sider door then will be the best option.
d) Most importantly, I already have a bar fridge for the shed, PLUS and old TV to watch the GPs (Moto and F1)!