The thickness of a scaffold board is 35mm and so laying the boards side by side (just like you would see on scaffolding) instead of using 4 by 2's will create an extra 60mm of much needed headroom under a section of my garage flat Roof. It would be a permanent installation. The boards would then be sheathed with 18mm ply and possibly edpm roofing material.
The area I wish to cover with said boards would be less than 4 square meters and the span lengths would range from 1.4m to 2.2m. All 4 sides to this area would be supported - ie. 3 walls and a beam. My thinking is that it might even be stronger than using 4 by 2's at 400 centres.
Is there any reason you can think of why using scaffolds wouldn't work?