You have to determine that for your house. Take graph paper, a set square, draw the width of the house and then apply the 35 degrees. Measure the height at the intersection of the lines. The wider your house, the flatter the roof can be to achieve, say, a 40 sqm area with a standing height of two meters. It is a planning exercise. Access with us is via a real staircase, not a floor hatch. Thus a raised basement. It is certainly cheaper than a real basement and trouble-free. Karsten