Update-
So, we finally have our ramp. We opted for a ramp built from "decking" material. The cost was equal to what we were looking into; and we decided that it needed to stay in place.
Ran it front to back, so didn't take up too much space; although we can't use that bay to park a car in. Luckily, we have a double car garage! But hey, the scooter needs a garage too!
So, to re-cap, 16' rise- we did a 10' ramp. This is a comfortable angle for Jim. (inspite of what Al says! He is a true dare-devil saying 6' is fine! LOL)
Now, inside we have a 12" rise in the sunken family room. We have a temporary ramp of 6' set up there. He can navigate this fine. However, last week he was going down this ramp & whoosh! I said, "What was that?" His answer, "One drink too many!" (he had 2 drinks!) So, we are considering an 8' ramp here!
I have posted pictures in an album for those who wish to see.
Again, just info for those looking into this process. Consider what works for you!