Additional map layers can be added to a RAMADDA install. Any plugin file (in your <RAMADDA home dir>/plugins directory) that ends with "mapextra.js" will be included in a bundled JS file. For example you can see the custom map layers on ramadda.org at https://ramadda.org/repository/map/extra/extra.js.

Here is a basic example of adding custom WMS and WMTS layers:
mapextra.js.example
Change the name of the file to mapextra.js

And here is an example of adding weather WMTS layers. This includes GOES satellite images, NWS radar and precipitation layers:
wxmapextra.js.example
Change the name of the file to wxmapextra.js