Many gazebos are 6- or 8-sided. Is that what you mean when you say "round"? If you really mean completely round, the level of construction difficulty will be substantially increased.

I mean hexagon or octagonal shaped, of course.

From what I have seen online when I was researching pergola and gazebo plans, there was nothing much of value available for free as far as detailed plans. There are a lot of good photos, though, and I used them to develop a design and come up with construction details myself. One site I found that has a lot of good gazebo pictures, and other helpful resources is in the link below.

Here is a link that might be useful: Gazebos

I build gazebo greenhouses in Alaska and the biggest I've made was a 10 sided greenhouse 26' diameter from point to point. I used an internet polygon calc to figure the length of the rafter runs and a perimeter cable to hold up the middle. I've posted some pictures of it on a facebook page listed below. Each side is 8' long so you save quite a bit on the materials and the rafters have a 5" pitch. Because it is all panelized, it bolts together fairly quickly when you go to set it up.

Here is a link that might be useful: Simple to Build Large Gazebo Greenhouse

There is not really much resource on gazebo plans online which is a shame. But I found a nice blog with some good ideas but no plans.

Here is a link that might be useful: gazebo plans