Looks like it needs insulation to me also, and ant-con heaters if not there. Also is that OSB / Sterling board on the roof? I personally think it needs some stiffeners, it usually starts sagging between free spans of 2-3 feet inbetween. Good advice re: windows, block them out straight away. And same with the doors, get those hinges fitted with round head bolts on the outside etc if not yet. Lastly -it's a catch 22: Never ever make a shed look like it has anything "attractive" or worthwile inside either. They will often get in regardless of anything you can think of (it's their professional job), but you can try to camouflge it as something "drab" and less interesting from the start. OTHERWISE I'm a bit jealous -would really like a shed / workshop to work in. Proper workbenches, proper lights and electrics with RCD sockets, can make a bit of noise and mess outside the house. Very envious!