Seen any decent sheds? I guess it must be a right mixed bag of quality online... I'm thinking 6' by 8' should allow a decent bike storage area with room for a stand and a desk. A bit of insulation and lining is also on the cards.
That's pretty optimistic, you'd have to keep it remarkably clear of anything else to actually be able to work on a bike in a 6x8, especially if you're storing another one in there at the same time. I've got a 6x8 and I can only just hang a bike by its front wheel under the ridge (although I do ride a 62cm frame), everywhere else the roof is too low. That means it sticks out into the middle of the floor, making other work in there almost impossible. Add a couple of spare wheels/tyres, a workstand, some tool storage and a trackpump, and various other odds and sods, and you're down to no space at all very quickly!
That's pretty optimistic, you'd have to keep it remarkably clear of anything else to actually be able to work on a bike in a 6x8, especially if you're storing another one in there at the same time. I've got a 6x8 and I can only just hang a bike by its front wheel under the ridge (although I do ride a 62cm frame), everywhere else the roof is too low. That means it sticks out into the middle of the floor, making other work in there almost impossible. Add a couple of spare wheels/tyres, a workstand, some tool storage and a trackpump, and various other odds and sods, and you're down to no space at all very quickly!