I know some people leave theirs on the floor, but I wanted mine off the floor to make shoveling out their coop easier. If you attach them to the wall just make sure they are lower than your lowest roost. A chicken likes to roost as high as possible and you want them to choose a roost at night, not your nest boxes.
I was told 1" off the floor with an attached perch in front
I think she means 1' (1 foot) off the floor not 1" (1 inch) off the floor. I'm not sure how you can easily sweep under 1 inch.
Anyway, she's right about the heavier breeds. I would suggest going with a lower nest box for them. And having a perch in front of them is a great idea to help the hens getting into and out of the boxes.
Some people have theirs on the floor and some people put them up higher. It basically depends on what works for your coop and if you want to lean over to pick up eggs.
I have heavy breeds and two rows of nest boxes (one on top of the other). The top row is about 2 ft. off the ground and the bottom row is about 12 inches off the ground. Most of my girls chose to use the top row.