@muhl Thanks. I will try to address some bugs and other interface oddities I found while working with your file.

That said, note that BEopt doesn't want you to draw the entire MF building -- just the MF unit of interest and any adjacent spaces that affect its heat transfer. See the help file and provided sample files for some examples. So, for example, you shouldn't draw the attic if the MF unit of interest has another MF unit completely above it. You also should never draw the entire slab/attic of the MF building, just draw the slab/attic adjacent to the unit and note where the slab/attic is adiabatic (i.e., adjacent to slab/attic from other MF units).

Here's an updated version of your project file that is how I would expect this MF unit to be described: Updated model