I have purchased three replacement covers for my costco frame over the years.
This is the only one that fit. It isn't as tailored as the others just a flat sheet with nylon rope sown in to pull it over the edge of the frame on each end but it looks fine that way we'll see how hacing no gromets on the ends holds up. The gromets to ancor it on the horizontal poles are in the perfect spot to pull the cover tight so water doesn't pool. None of the story that you need a 12X20 to fit a 10X20 only to find that it's not the case, nice job. Though I could do without the large shelter logic logo on each side. 

Pros: Fits the Costco 10X20 frame perfectly
Cons: Large logo on both sides. No gromets on the peaks or skirts