Way to go , Some of the 'Office' Rooms are nuts prices, Was Looking at a Steeltech option myself and get rid of the Portacabin which is too damp. Your shed kitted out with insulation etc will be nice and toasty!! About 10K for a 20x10 Steeltech yoke and like you would have to do the base.
With re bar no fear with Nuke strikes!!
Oh a lovely Stream next to it too, Wow, only Perfect!