Zandronum

I was just wondering, i wanted a bridge in my mediocre map [started creating single-map .wads a year ago after trying to see what i could do with gzdoom map editor], but i've wondered if it's possible to stack a 3D Floor [standard, opaque solid] on top of a deep water 3D Floor

You can stack a 3D floor bridge over 3D floor water, but you cannot stack a 3D floor bridge over transfer-heights water. Beware, though, that 3D floor water is much more expensive, potentially causing FPS lag.