Only put lino draught excluders on the top of each door so far. Not sure how I'd fix it to the bottom of the door. Thinking of using a more solid rubber draught-excluder for the floor instead, but want to sort out insulating or getting matting on the floor before then so I know how much of a gap there will be.
The doors themselves have metal strips on each side which cover the gap (see pic), into which I plan to put a regular window draught excluder/thin rubber strip.

I've nearly finished insulated the roof. Cutting Celotex with a kitchen knife creates far less "dust" than using a saw. Still takes an age though.
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Looking at doing the walls next. Planning on a mix of battens/50mm insulation/board for where I won't need to hang shelves, and studs/50mm insulation-infill/insulation-over/boards where more strength is required. Then I should be ready to start something more interesting.