Buy this. Everything is beautiful and easy to use. For me, at least, it made Roll20 finally worth using.

The creator also was kind enough to provide some tips in setting it up on Roll20, which I will reproduce here:

"Ok here is what I use for page setup:

• set page size to 100 x 100 units
• set unit size to 3ft per unit
• Hide grid
• I drop a blank background into the map layer, then build in the token layer, I start building in the top left and work my way down. Once I get a good layout i drop everything into the map layer. if parts appear to vanish select the background layer right click and send to back.

here is an example of it all working for you to check out https://app.roll20.net/join/2461812/SVsmRQ"