What can I put under my outdoor bar and gazebo?

Phyllis, would you be a little more specific about your issue/request? I'm not sure where you are going with this but I would love to help you.

What is out there now?

Do you mean for flooring? https://www.hgtv.com/design/outdoor-design/outdoor-spaces/12-outdoor-flooring-ideas-pictures

we have a gazebo that we finished off with concrete. when we got tired of that hard surface, we found some rubber tiles about 18" squares and a heavy weight. These were from a surplus store (Ollies) and we had to visit several, but these are holding up well into the 2nd summer. A nice cushion too for walking on.

Indoor-outdoor carpeting might be a help?

I would use 18" x 18" patio blocks for this project. Level the ground as best as you can. Then lay down an inch or two of sand. Then lay down the patio blocks. Best of luck to you.

Phyllis, typically, you might find a cement, concrete block, or wooden deck. You could use indoor-outdoor carpet over wood or cement, or dirt and sand underfoot. If you want tile, again you will need a cement or wood deck underneath. Best wishes ☺️

If you are thinking about flooring, you can get squares of wood decking to put beneath them.

Concrete Floor Slabs.

Cheap floors would be pea gravel wood pallets.