I have a garage with a deck on top of it and need to replace all of the wood. The builder built 4 "pallets" and placed them on top of the roofing material on the garage. The deck is 16' x 16'. 2 Pallets are 7' x 8' and the other 2 are 9' x 8'. The reason I use the term pallet is because that is exactly what they look like, except for the fact that a pallet is made up of three sections: the top and bottom mirroring each other with a smaller cross-section in the middle. My deck does not have the bottom layer. The sections sit on the roof top and are able to be moved quite easily. My questions involve what I have too look out for in the way of runoff for the unprotected roof (Chicago winters). I want to use 16' boards instead of 2 sections. Please let me know what you can offer in the way of advice in replacing the wood in this configuration. I expect many questions to ensue regarding this post, and I fully appreciate the help.

Thank you very much