I spent most of a day making these and in hind sight, and would not do it again. (Pic comes from an old posting on here I think)? You'll need four. If you go with one long ramp for each side. They get really heavy, and really, really heavy when they get wet. Not to mention the mud. I would stay with something that is easy to clean and not wood.
Anyway, after thinking I would have something I could use for many years, they did not last. Wood started cracking just after a couple years, then they really fell apart. Your luck might be better.
If using where you park, like at your house they might last longer and one piece ramps for each side might be OK.

