I have two Midwest cages with the "remodeling kit" from Kritter Koncepts.
( www.kritterkoncepts.net)  By the time you buy a couple replacement
shelves and ramps you could buy the kit.  It consists of three floors
with connecting ramps, made of heavy vinyl coated cage quality hardware
cloth.  1/2x1/2".  The ramps can be hooked up to close off a floor to
divide the cage if you want, and the ferrets get actual floors.  I did
have trouble with the size when I sent for one so be sure to send acurate
inside measurements.  You get to install it with cage clips and once in
place the cage does not collapse.  I have kept as many as 6 ferrets in
the cages this way.
 
For the floor I replaced the original trays with plain flat trays from
Martin's Cages 24x36 Dura-tray.  I found they must be set of a solid flat
surface like 1/2" plywood on a table to support the weight of the cage or
the cage will push it down and out of shape.
 
Carol
[Posted in FML issue 5151]