Ya I'm per room also, I like Jonathan's pricing and reasoning putting the customer in control.
We just went to $35.00 a room with a 200 sq ft limit, $15.00 for halls and $10 for walkin closets, and bathrooms. $3.00 per step. Pet odor and stain starts at $10 more per room red stain are extra too.
Commercial depends try for .15 cents minimum been doing a 20k church 2x a year for .10 cents but that's filler work after Xmas. And August.