Ozodrin doesn't say anything about levels affecting how big the stomach is. The only thing that increases that is the Large Stomach augment. Without that, it will always be able to hold 1 huge creature (or 4 large, or 16 medium, or 64 small, or 254 tiny,or 1024 diminutive, or 4096 fine). Using formed stomach, this means that default "house" size is 160 5x5 squares (with the ceiling 5 ft from the floor) (320 squares with 10 ft ceiling with Expansive Stomach). If you want for stomach size to scale by level, you should add something to this affect:

Expansive Stomach (Ex): A menacing manor's stomach base size increases by 1 2 creatures every level. In addition the stomach of a menacing manor has twice the capacity of other ozodrin. Any additional stomachs that it would gain using the stomach feature similarly start at twice the size (increases to their size happen at the normal amount). If a menacing manor would die, it's stomach petrifies and remains in the form it was in at the time of the manor's death rather than decaying and ejecting all creatures inside.

where 1 is a number and 2 is a size category.