An owner or GC asks for a ROM to test a budget. The design may be a sketch, a floor area and a short description.
A flooring sub might price a ROM from the gross floor area. The cost per square foot comes from similar past jobs.
State what you based the number on. List the area, the finish level you assumed and what you left out. Give a range and say it is not a bid.
Keep your notes. When real drawings arrive, compare them to your assumptions and explain the difference.