If it were me, I would do exactly what you mentioned, a shelf that doubles as a hidey house or space to sleep under. If the total height of each level is 24 inches, make the shelf the depth of the condo, 12 inches tall, and maybe 12 inches wide. That will give enough space to jump onto, jump off of, and lounge on or underneath.

Ramps make a large amount of room unusable. Winston’s cage has 1 level that is 13″ with 12″ of clearance underneath. His litter box is under the step and there is plenty of room for him to eat and potty… plus, he likes to hide there when my kids get rambunctious.

Winston is an average size Californian neutered buck who has a old front foot injury limiting its use and he has zero issues leaping up and down from his platform.

Ramps have worked well for Porky in his condo. I set them up in a spiral configuration, and it lets him zoom up and down from level to level. It gives him a much longer distance to run than he could have other wise.

When he gets excited b/c he thinks carrots might be coming, Porky will run in from his porch (an ex-pen like open area made from NIC grids he has 24//7 access to) go round the first level at break neck speed, up the first ramp, round the second level at break neck speed, up the second ramp, then hop into his litter box when he gets to the third level. Up on the third level, he periscopes sniff the air then zooms back down to the second level from which he flies out the normally open condo door and hops about his porch binkies once, then stands there begging for carrots. If said carrot isn’t handed over within 6 sniffs he repeats the whole sequence.

Porky isn’t much of a jumper and I doubt he would much utilize his upper levels if he had to jump more than maybe 8 or 10 inches. Though he will jump out to his porch from the second level of his condo, he only enters it from the first level unless he has a step up and then he does it slowly.