I'm thinking of building pergola/arbor freestanding so I don't have to attach it to the house. The problem is the spans I need to cover to avoid placing posts in front of windows.

The spans I would like to use are 12'8 between the first set of girders, and the girders themselves would be 16' long (or at least the patio is 16' deep;the whole patio is 16 x 32 rounded off at one end). So the rafters would span 12'8' across the first set of girders. the other rafters would have much shorter spans.

Basically the first section would be 12'8" x 16'.

Can I do this? if so, how? what material to use.

Thanks