A family house from 1996 with nine internal doors to replace, where the owner had already bought nine standard doors and found that not one of them fitted.
We measured the openings. The widest was seven hundred and eighty six millimetres and the narrowest seven hundred and fifty one, and three of the frames were out of plumb by more than ten millimetres over the height. Standard doors could have been trimmed to fit six of the nine, and trimming a flush door removes its lipping and exposes the blockboard edge, which then has to be re edged by hand at a cost approaching the price of making the door.
So we made nine doors to the nine openings, in blockboard with a sprayed finish, and replaced three frames that were beyond packing. The bathroom door went in a hardwood frame with a sealed bottom rail rather than the softwood frame that had rotted at the foot.
The owner sold the nine shop bought doors to a neighbour, which softened the arithmetic. Two weeks, and all nine still close with one finger.