Not enough nesting on the floor?
Wont the egg crack?
They need padding on the floor!
Not to worry, as you can see from this picture from Mel and Sydney's first clutch the floor looked about the same as it does now.
Barn Owls do not "build" a nest but just before egg laying the female usually makes a shallow scrape in the previous years' nest debris and/or breaks up a few recent pellets creating a soft layer for egg laying.
Many owls lay their eggs on the ground or bare floors.
Barn Owls in Africa use the giant stick structures made by Hammerkops (a stork like bird) occasionally nesting communally.