I am contemplating an extension to my single storey kitchen, which currently has a flat roof. The extension is to be wall to dado height, or thereabouts, with UPVC windows above, all round (two sides). I have had brief plans drawn by a friend, and understand that approval is unnecessary as the extension is small enough to come within new rules. I am planning to subcontract the work to save on cost, and am not sure how to go about getting what I think should be tubular steelwork frame to support the roof, these will have the UPVC windows fitted inside. Also I am a little concerned on the pitch of the roof as I have limited height to windows of main house. Can anyone point me in the direction of any reference material for these queries please?