But if you were earning £27000 you wouldn't even get in the door of the bank looking for a £423000 mortgage even if you had your £27000 deposit in tow. In reality you would need £25000 to buy a £150000 house and then you are pushing the bank to over 4x salary for the mortgage. Its all madness...
Sorry missed that one. The 'from' prices are just steel frames, so columns, rafters and wind bracing. on a 30ft span we would be 203x102ub columns and rafters and 88.9dia chs wing bracing to roof and sides.
Whats your height restriction with composite? You would probably be looking at 120mm+ to meet u/values for a house.
You could build it like a chicken shed, fit purlins between the rafters, underline these with ply or maybe foil-backed boarding, Rockwool the rafter viod, then put a tin sheet on top.