Hi I'm building a 5 x 12 foot shed and was wondering what the dimensions of lumber for ridge board to span the 12 feet so it can be an open area

Bit strange shape tor a gable roof. 5/12 pitch would use a 2x6 ridge with 2x6 common rafters measuring less than 3' each. For a 5' span you don't need a ridge, just plywood or OSB gussets and a collar tie or two. Can't build a shed roof? Much less lumber, cutting and design. Just finished a 4x8 attached shed roof storage shed . Took 2 of us less than 4 hrs. Don't need a ridge, just a wall plate. If you can read a framing square fairly easy job.

I have odd requests but my problem is snow and I can't change the dimensions. I don't know the structural qualitys of the lumber. You think 2x6 12 feet long would be good because I need the open area. It's only 7 feet tall at most

Bit strange shape tor a gable roof. 5/12 pitch would use a 2x6 ridge with 2x6 common rafters measuring less than 3' each. For a 5' span you dont need a ridge, just plywood or OSB gussets and a collar tie or two. Can't build a shed roof? Much less lumber, cutting and design. Just finished a 4x8 attached shed roof storage shed . Took 2 of us less than 4 hrs. Don't need a ridge, just a wall plate. If you can read a framing square fairly easy job.
Sorry new to site but have lumber for anything just don't want beams just want it to be open want the rafters and ridgeboard to support 2 feet of snow also and can't change dimensions it's all the space I have and actually need it bigger

I wouldn't use a ridge for 5' span. Not needed. Use 2x6 joists with OSB cleats and a.collar tie at 4 and 8 ft. You are going to have headroom issues with a gable roof that is only 7' high.

Problem you will have is headroom. With a heavy snow load you need a 7/12 pitch or higher. Starting with a 7 ft gable height is going to drop your walls down. Can't do 8' walls?