One thing I've used in VTTs online quite often are repeating textures (small images that can be placed next to each other infinitely), and generally the way I see these implemented is as an addition to the draw tool or whatever variant that VTT has. Such that instead of drawing in a black 2x2 box, you might draw in a 2x2 flagstone floor using the flagstone floor repeating texture instead of the color black. I haven't found a way to duplicate this functionality in Roll20 yet so I can only assume that it isn't currently supported - if it is, sorry, I guess I wasn't thorough enough.
However, if it really isn't supported, I think this would be a great feature to add to Roll20 because you can store these repeating textures in an extremely small size (they're only a couple dozen pixels per side image files) while their use is really huge since you can draw in the floor of a dozen rooms just by repeating this image file using the draw tool. That would give a user with access to such repeating texture images (which are pretty easy to find online) a way to have a lot of options for drawing things while still not taking up a lot of storage on their PC or the Roll20 servers.
In short: I propose, if it's not a feature I just couldn't find documentation for, that the draw tool support images as well as colors such that you could use the draw tool to draw in a floor rather than just a solid color. For a good example of this kind of support I can refer to Map Tool, which has just such a feature and in my experience it's very handy for building custom locations visually.