Usually “billed to G&A,” unless you want it to escalate automatically as you hire new employees, in which case you would determine how many square feet each employee requires, multiply it by the average price per square foot of appropriate office space in your community and enter that in the boxes along with “per employee.” Obviously the former approach works better in a retail or wholesale setting; and the latter works better in an R&D setting.

Related Question:

How do I add/change rent expense?