Hi Sopheap,

It's a good question, but I would say that it is not appropriate. The Mixed-Use Standard states:

This mixed-use standard is intended to be used in conjunction
with these five standards (office, industrial, gross, residential, retail) and does not replicate their
content. All except the BOMA Gross Area Standard are single-use standards intended to be applied to buildings (or a portion thereof, such as a use component or parcel) that are occupied by a single primary use.

also:

If the primary use does not fit within the scope of any BOMA single use standard, apply the BOMA Gross Area Standard to determine the exterior gross area of that use. Refer to the appendix for a list of specific uses and the appropriate standards to apply.

I can't find anywhere in the document stating that a single occupant office use component can use Gross Areas.

You could consider simply using the latest BOMA 2018 Gross Areas Standard for the entire building. That standard encourages areas to be broken up and separately disclosed, so you could report all the areas in the building however you want. However, not using the Mixed-Use Standard could have drawbacks as it does allow the proportionate allocation of Mixed-Use Common Areas to the various Use-Components. This really only impacts the rentable areas of the office-use components and industrial-use components though, since the other standards don't include a proportionate allocation of common areas.

Thanks,
David