Hi @ctomayer - adding area types can only be done by creating a custom module right now.
For an example, see the “Farm Livestock Area Types” module that is included with farmOS: https://github.com/farmOS/farmOS/tree/7.x-1.x/modules/farm/farm_livestock/farm_livestock_area_types
The other caution I would add: we are thinking about changing the way Area Types are defined in farmOS 2.x. So if you create a custom module now, you may need to refactor it when it comes time to upgrade to farmOS 2.0.