We are using standard IAB ad specs on this site, so if you already have ads designed, they should fit right in. The following is the list of the IAB standard sizes.
Horizontal Online Banner Ad Sizes
728 x 90 Leaderboard
Rectangular Online Ad Banner Sizes
300 x 250 Medium Rectangle
Square Online Ad Banner Sizes
125 x 125 Button...
Years ago, when I began working fulltime in the production and post-production industry, I was fortunate to have access to a local organization that was composed of media professionals, shooters, editors, graphics, sound, and many more fields were represented. I have made quite a few lifelong friends from that group.