Just thought I'd post a quick update. The shed has been built, insulated, etc and is having its electrics wired (Part P certified) next week!
I've been blogging about the entire process so that if any other DIY newbies ever plan on doing something similar, they can find out what I managed to cock up and how not to do it!
If anyone is interested I've got the blog up (and a large number of photos) he
Building The Garden Office
(Note: There are no adverts or anything like that - I make no money from this)