The only things you have to know about making a map for VTTs is:

  • Do not put in a grid
  • Make the map to a scale that will work with the VTT. Typically this is 200 pixels = 5', but honestly VTT software is able to handle pretty much any resolution you throw at it just make sure that you mention the scale somewhere in your posting so that folks know how to scale it in the VTT.
  • Everything else is no different than making a regular map, and in fact the two items above really aren't that different either.

As an aside, if you intend on sharing the objects/tokens and a blank map make sure that you use layers to make it easy on yourself at the end.