I have an ambitious plan to build a workshop. It will have a flat roof and I'm considering a GRP covering. I found an excellent YouTube how to for the GRP bit, just need a bit of help with the fascia and soffit detail. My question is what to do when joining the fascia to the roof joists and how to mount the soffit to it. I believe I would need to use vented soffit to allow air movement around the joists and I will only use it on the front and back of the building as this is how the joists are running. There will be no insulation between the joists, the walls will be cavity construction. As far as I remember, the joists will sit on a timber wallplate and be connected with a plate hanger on the internal wall. I will be using uPVC fascia and soffit and tbh, I wondered if there wasn't just some type of venting strip I could use in place of soffit board. Thanks in advance for any suggestions, links to drawings videos etc