Ok, so I've been researching and looking around at NIC condos and I've drawn up some some sketches from other condos I've seen. The only Thing I can't seem to understand is the condos that have the levels but don't have the dowl rods or wood sticks that go on the sides all the way across how they are supported? I see a wood stick or dowl rod in the middle of the side going under the level but I don't see how it supports. I've tried looking at all the picts but it doesn't show pictures from the underside of the levels. If anyone wouldn't mind taking a picture under the levels of how you support them (if you  can) or explain that would be of great help!!  I see some condos where the dowl rods (2) go on the front side and back side all the way across but I was hoping to have more of a hidden look as much as possible. Also some where the dowl rod or stick goes from the back to the front of the cage across the open end of the level. I hope my description makes sense

The edges of the NIC cubes form walls, and the walls that are perpendicular to the ground bear the weight and keep the structure up.  It is kind of hard to explain, but think about taking a carboard box with no top and turning it upside down.  Now, if you put something on top of the overturned box, the sides of the box support that weight.  You have to zip tie or secure the panels together pretty tightly so that they reinforce each other and don't shake too much.

The dowels/1x2s that you see are to support floors.  If you zip tie four panels together in a square, then pick it up by the edges, you'll see that it sags in the middle.  The zip ties do not offer enough support to allow direct weight on a conneciton like this, so the dowels are used to offer support to the middle part of the floor.  1 1/2 inch dowels or 1x2 lumber will snap right into the perpendicular walls of the condo, and if you slide them across the middle of the floor, they become braces, and no sagging.

My NIC condo:

3 platforms:

2 x smaller (~2 grid squares large)
1 x big middle floor (~4 grid squares large)

The platforms are formed from dowel supports and wooden platforms ONLY (thick plywood/particle board things [don't buy the thinnest or cheapest, get it thick and heavy enough so it doesn't move and rattle if your bun decides to do a bunny 500 in his condo])

Grids ARE NOT used to form the levels.

2 x smaller platforms supported by: two dowels (each) going from front to back (one large dowell cut into two halves)
1 x large middle floor platform supported by: two full-sized dowels running from left to right, spanning the width of the cage.

Pics to come tonight or tomorrow.