A low cost roof which instead of using standard roofing, uses PV panels that have a gutter system making the PV panels function as a water-tight roof. The advantage is using building-integrated PV to provide the water-tightness function typically provided by a standard roof. This is done while avoiding the cost of the standard roofing material, at $4/sf cost  This produces value in energy which pays back for the PV and roof cost in 2 years (2 year payback time for PV) - effective providing a free roof. The up-front cost is 2x that of standard roof (PV costs $8/sf ).
Roofing detail for a 'roofless roof with solar panels', v2. - File:Roofless.fcstd.
Roofing detail for a 'roofless roof with solar panels'. v1. - File:Roofdete.fcstd.