Wood Huh! Well OK! BUT, if you don't use treated, it will be rotten in 3-5 yrs. I know, it happened to me. I think you could use 4x6 treated for the main rails. I've never seen 4x8. Must have to have them cut at big mill. They won't be smooth if you go that route, stick with the treated at most good yards. Think you may be able to get 14 ft too, but sometimes longer ones move faster and you can get better wood picking 16's. You can always layer 2 x's and get good results also. Much like a beam in a house would be. I would recomend 2x6 treated tongue and groove for top boards. The 5/4 decking won't be strong enough and give over wider spots, and when it shrinks it will leave gaps. Most treated will shrink and leave gaps, the tongue helps some there. I once temporarily bolted on my treated wood and left thru winter, went back in spring and unbolted, pulled it all tighter again with big pipe clamps and rebolted. OH, Yes, this was after I painted the boards on all sides dissassembled including the tongue and groove part and them put back together. Had to leave last board till done to cut to right width. Clear as MUD? Treated lumber now has new "safe" treatment, no arsnic, costs more now too. You can paint it, but they reccommend waiting for year or so, to dry good. You'll have to run ground wires for all your lights to frame or somewhere too. I use those new rubber light holders and metal frames to slip in the new one-pc throw away lights like new trailers and trucks use, very nice.
