Ok, I am a novice at timber framing. I have an add-on project to replace an aging sunroom. I plan build a 18x20 on a slab. I have designed a 3-bay, 6 feet between, 20 foot clear span, 4/10 pitch roof all out of red pine center cut timbers. 1x10 treated sill against concrete, 8x8 sills, 8x8x8' posts, 7x10x20' tie beams, 8x8x10' principal rafters, 8x8x8' collar ties, 3x8 braces on corners and 3x8 arched braces at collar. I would appreciate any feedback or suggestions.