I have a suspicion about why the Properties panel doesn't allow you to add levels.
In FormIt, you can double-click on an object, like this building, and it will select only that object. But if you window- or area-select the solid, you'll actually get more than just the solid building, which is two objects, and the Properties panel won't be helpful.
There's a great plugin I built called Properties Plus. You can find it in the Plugin Manager, if you search for Properties:

That plugin will illustrate exactly what you've got selected. It turns out, there's another piece of geometry somewhere in the building, a LineMesh. Properties Plus tells you this if you window- or area-select the building:

So, a couple of options, if you run into this again:
- Select only the solid (body) by double-clicking it
- Or use window- or area selection, and use Properties Plus to unselect the LineMesh or other object by clicking on the (-) button to remove it from the selection.
- Alternatively, deselect the Body, keeping only the LineMesh selected, and delete that for cleanup.
Hopefully this helps a bit more. Properties Plus is a great plugin and worth using! More helpful than a blank panel in this case. 😁
Josh Goldstein
Senior Product Manager