I would say it depends on your knowledge of the construction and materials requirements. The ability to keep it clean would come into play as well. Plexiglas strong enough to support the weight you are thinking of would be outrageously priced and unless you have access to a piece that is reclaimed from some dance floor out of the 70s and already sized would make it hard on any budget. Structural glass in that size is a budget breaker too. Both would be subject to surface damage that would shorten its life and viewing properties.

What you put on it would be a problem. My DH would throw himself into a chair and shatter or at least crack it the first time he sat down. He doesn't sit, he drops. At 230 pounds that is a lot of pressure on the bottom of a chair leg where it comes in contact with a surface. He has broken slate flagstones that way.

I can see ways to get around some of the problems but what you have drawn up would be outside of the means of most people.

It's kind of like me loving museum quality paintings. Even if I had one, free, I couldn't afford to take care of it.

Width and depth of the island will make a big difference here, as well as the materials (pontoons/floats vs straight wood or metal). I'm not sure of the math, the main thing will be how well you can make it float and how much it will displace with added weight, and how well it will keep it's balance (you don't want it to tip over if someone walks to the one side). You're intending this to hold a lot of weight.

Have you considered making it more of a pier (frame with pillars to the bottom as a base) or depending on the size maybe a bridge (overlaps on the ground on two sides)? I think this might be a bit more stable.

And I agree with SleeplessInFtWayne, weight and cost of the glass will be an issue. I think there are ways to reduce this (instead of full glass panel, you could do a solid floor with windows tiled into it).

The same thought occurred to me about the windows but I keep coming back to the cleaning. The windows would need to be removable.

Thanks for the input. I figured i was being delusional lol but it never hurts to ask.

Oh Ashlie, it isn't delusional by any means. You just put a sensible restriction on it. There are many people in this world who go through life throwing money at any problem.

What about a rectangle of safety glass under a glass table? Then no one would walk on it, and you could still look down during dinner and watch fish. I don't know if it would be enough bang for your buck.

Perhaps decide what you really want from the glass floor, and figure another way to reach that goal. Is it views of fish? The perception of being right in the pond? A fun, slightly daring gathering place?

I really like stepping stone columns, little islands, that you walk on to get across a pond. They look so cool and would be very fun way to reach the gazebo -- and since your pond isn't built yet, you could build it cutting off a corner or edge of yard, and you'd have to get over there via the stepping stones. Woot woot!

I was thinking maybe i could do one of those koi domes but on a larger scale and in a rectangle to use as a table in the center of the gazebo thingy and that would be kinda cool