Is it okay to have 8' support columns on only 4 sides of the octagone gazebo? I want to space the posts every other one. The posts are heavy duty perma cast posts.

If you are working from an engineered design, omitting half the support columns is not acceptable. The columns support jack rafters or beams which hold the remaining roof in place. There may be alternative ways to brace columns and support the roof load, but departing from the designed specifications could compromise structural integrity, wind or snow load ratings and would have consequences on the transfer of load through the columns to the foundation.