The shed kits often put a bit of treated wood along. Roofing battens (laths) are treated and cheap but you may want to pre-drill them so the screws/nails don't split them.
If you have any roof seal handy, that is pretty good at stiffening up the felt. Nailed felt often leaks a bit of water at the nail holes and I like to seal them up anyway.
Last edited by diggingdeeper; 30th Jan 2018 1:20pm.