In reply to abr1966:
I got one from Winchester Garden Buildings (I think) 4mx2.5m was about £1500 including windows, work bench and double security doors and hard standing to sit it on. In all I think I spent £2500 adding electrics, insulating shelving and boarding (which I did myself except the electrics - extra fuse box in the house and buried armoured cable to the shed).
I'm sitting in it now its great.
Have a look at https://www.gardenwave.co.uk/ if you want something a bit different (and a bit more ££) my Cousin makes them (he didn't do it when I got my shed)
Post edited at 19:21