I built mine with the 143 as well -- needed a ladder for building the 3rd story! I didn't think at first they used it that much. But since I had Bass pans, I took the original black plastic bottom tray and inverted it on the very top of the cage (to make it "darker" and covered up there). Well, judging from the number of poopies collecting there on Level 3, it is apparently their favorite nighttime hangout. I have mine set up as follows, all with Bass pans:
Level 1 -- Aspen shavings, flying saucer, hay racks, hay cubes, hidey house, water bottle -- the MESS zone
Level 2 - fleece liners from PPBN -- the SLEEP zone -- couple of houses/hideys, chubes, toys, toybox, water bottle, food dish
Level 3 - fleece liners - the PLAY zone -- toys and more toys like hanging gardens, PVC tubes/tunnels (also from PPBN), sleeping cot, feed dish
On levels 2 and 3, I kept the half-shelf FN balconies -- they don't chew on the plastic and it gives them another level. Took it off the bottom unit till they get more used to the Flying Saucer
I like it so much myself, I built a second one and acquired four more boys to fill it! I just finished it -- the stand braces were missing from the box, so this one does not have the stand on it at the moment, till FN sends me the missing parts. Not sure which way I like it best!