Finishing basement. Question about adding Sq Ft.

[Billy Farley]

I am purchasing a fix and flip here soon and the basement is fully unfinished out. There are some electrical units and dry wall put up, but mostly unfinished. I am planning on minimally finishing it out buy painting/epoxy the floor and making cement walls look nice and general waterproofing (looking for advice on that). House is 826 sqft upstairs, basement is 826 sqft but unfinished with the utility room as well as a room with small basement windows (not egress). 

I want to list it as a 2bd 1 bath 1600sq ft with bonus room (office/kids room). What do I need to do so that I am covered when listing like that. Who makes it okay to list as finished space, what are the requirements. We do all our work in house, (have contractor as partner), and are considering running HVAC down there. 

I could really use some insight as this is my first flip. If you have any more questions about this scenario, please ask!