Does anyone know where I can find a complete vectorial database of the 3D building footprints (x, y, z, or building height) of the USA? At a cost or free.
Two things spring to mind. Unfortunately these are building footprint datasets, so they mostly won't include building heights. There are ways around this at smaller scales, you could do zonal statistics on a digital surface model for example. But I'm unsure how to proceed for an area as large as you're seeking.
First off is Digital Globe's building footprint product; https://www.digitalglobe.com/products/building-footprints
This is definitely a paid for product though and likely to get expensive quickly when you want the whole US.
Secondly, Microsoft/Bing's US Building Footprint dataset here; https://github.com/Microsoft/USBuildingFootprints
This is completely free for the whole US. Unfortunately the building features don't have any attributes, so again there isn't any height information.
I feel it is important to point out that just because these datasets don't have height information it shouldn't detract from the massive achievement that is automated building extraction across continents.