I was just thinking about making a mod request for a different way of faking z levels.
A building that looks like a tunnel called "Tunnel that goes underground" once 'constructed' colonist will disappear (hopefully) into an imaginary underground tunnel where things can be stored and retrieved. However, you would never see anything in there except in the list of items stored and who is currently retrieving from there. Much more simplistic I'm sorry to say and a little off topic, but still an easily made mod that should make your colony feel more roomy.
Potential fancy features: Can chose closeness to "basement" entrance (reducing time to extract items), requires mining skill where appropriate, Can expand it 'infinitely' by sending a miner in ('walking' time cost will increase), Can get mine able resources out of it at appropriate rates (perhaps with options to dig around plasteel for a time), include its room size on your room wealth thingy (if that's a thingy), allow infestations to occur down there (which you would only fight outside the mine/storage area), add a small micro menu that actually allows you to see it (so not "never").
Great realism, use, and ascetics.
Jaxxa, Don't know how you could do it, but we are all rooting for you!
Jamaicancastle, Sounds great!