You can use maps other than 10x10 if you use the verticalLevels definition on a facility instead of the mapName. However, that still won't get you to making a 120x120 base defense map unless you do some very fancy and long map script.
The map script would need to be something like:
- Use checkBlock + either groups or block numbers to figure out where the normal code to place facility maps placed what map. You'd need (# of facilities in your mod) * (# of positions where a map can be placed = 36) different checks, each with a unique label.
- Remove all the facilities that were placed by the normal code.
- Resize the map to 12x12.
- Have an addBlock command for each unique label from step 1 to place your double-size facilities at the correct locations.
- Dig the tunnels between facilities.
- Fill in with dirt.
If you're okay with having the base defense map not match the base itself (your players would hate that!), then you can simplify the map script by removing the check block portion and making it more like the alien base script. However, you'd still have issues with the code trying to find where to place the items in your storage facilities, since those positions in the 60x60 map won't match where they should be in the 120x120 map.
In short, don't do this. Find a way to not need a 120x120 base defense. It's not supported well at all and few players would enjoy it.