I have actually done this, twice!!
Check for building regs limitations
New roof, including joists, insulation..
Doors, windows
Damp-proof floors and damp proof course in walls
Check and fix new where necessary drains, manhole access, etc in acc to new regs, do land drains go into neighbouring properties and do you have permission now to have them there (minefield, trust me...:incazzato
If there is an extension, if it's single breeze block, knock it down and get new foundations for double breeze block insulated walls to take 2 storeys
Check staircase, new or old, for compliance with building regs... often they are too steep for the new laws... you don't want to find out afterwards..
Plumbing
Electrics
Flooring
Heating
Making good the walls (new or old ones :lol
And then the nice staff starts... new kitchen, bathroom, plastering walls... choosing pretty things... the order of things may change slightly depending on circumstances re drains etc.. but the roof is the main thing to make good first.
Good luck, look after your back and knees