I'm looking for creative ideas for the interior of a 10' x10' gazebo.?

If you want anything painted glossy, use oil or alkyd based enamels, not latex.

Concrete items are weather-proof. There are many small concrete ornamentation you can buy . You might have to go to a mason yard, or independent lawn/garden/landscape center. Home Depot doesn't carry them. And if they did, you'd wind up with the same one everyone else has.

Also, old cast iron / wrought iron things seem to hold up well as decorative items. Knobs, fixtures, even furniture. Coating them with linseed oil will usually keep them for over-rusting, leaving that nice "old" look, if you don't feel like painting them.

Sections of old stained-glass could also work.

It really depends on what look you are going for. Thinking of a theme, and going for it, usually winds up looking better than the eclectic approach... in small areas anyway.

For ground cover, I would definitely consider an outdoor rug. You can get some beautiful patterns and can find them large enough to cover the whole area. You might also want to consider outdoor curtains that you can open and close to adjust privacy, light, or temperature. There is also some beautiful patio furniture on the site below.

In ours wa have a round table in the center with chairs around the perimeter. A small chandelier in the center with a dimmer for light. ours is screened in and wa have bamboo shades to be closed for privacy at night or to break the wind on cooler days. My dad built ours its 16 x 16 with 10 sides.

Being in newengland, we have plywood sides we put up before the snow flies.