Mattn,
Not sure if the issue regarding being able to build base maps according to the actual layout the player installs the items on to the grid has been resolved yet. If not, perhaps there is a solution.
If an x and y parameter were added to the ump build scripts for the tile items (tile min max specificx specific y), and you located where in the grid they were to be built directly, you would be able to 'randomly' generate a 'real' map. This build script would have to be built on the fly, but it might be an option.
Unfortunately I'm not entirely sure how the Random Map Generator engine fully functions, but I'm hoping this might seem feasible since you were recently working on it.
