If it's quite a tight space, a good option can be to go for steps rather than a ramp. That way you can go up quite a steep angle over a short distance, but it's much easier for a bun to do.
It would depend on your bunnies, I'd say around 6-8" would be very comfortable but a lot of bunnies could manage a bit more. Another option is a combination so you have a box a the bottom the ramp goes to that way you don't end up with that space right at the bottom under the ramp that isn't big enough for anything. Or you can have a series of shelves that double up as sitting spots.
I like the idea of shelves as sitting spots. Hope it doesn't rain on Sunday! Thanks for the ideas
Its supposed to be dry in our neck of the woods on Sunday!
BBC weather doesn't look good... I have a coat. Actually, I have an old nibbled coat saved especially for cold rabbity days
I think I am mad!
Using decking planks you can make them quite steep, although this example isn't very steep: