if they go up to a flat surface you wont be able to drive off them unless we are talking landrovers ! (not cheap but 4 post lift would be cool)

Looking at the pic's posted of the display 'type' ramps, I would think that to clear 4' you would need something twice the height, to gain access to an x distribution depot.
Something much longer and higher, would be required, which in itself will present problems with handling, eg fork lift.

IMO much better to consider a lifting platform of some sort, drive on/drive off, if used as a permanent storage facility.:thumbs:

I once dead lifted the back of a fiesta,

I've been told its only a couple of feet, but would still need long ramps.
It's for both the CSL and fiesta Shane.
I've been offered bigger and better (free storage)

I will measure it up properly when I'm allowed out ...

:hahaha::hahaha::hahaha: