There are a number of examples on the web of insulated cabinets for fermentation, which keep ice in a separate compartment from a fermentation bucket/carboy, and use a fan with a temperature controller to circulate air and thus regulate the fermentation chamber.  Perhaps the most popular example is the Son of Fermentation Chiller.  Quite practical, but living in an apartment, I wanted something a bit more presentable.

I was then inspired by the 38DD Mother of a Fermentation Chiller , which is the same basic idea but built into a nice wooden cabinet.  Again, living in an apartment, I didn't need anything that large, so I built mine to fit a single bucket/carboy.  Everything was purchased at the Home Depot.

The central frame consists of 3 square pieces of 1/2" plywood separated by pieces of cheap 2x3 studs in each corner, forming the bottom, carboy shelf, and top.  Then everything is sheeted with hardwood luan plywood.  The door is framed on the inside with 1"x2" pine. 

It's certainly not what I'd call an exceptional example of fine carpentry, I'm not exactly an expert and don't have much of a workshop.  I built it with a cordless circular saw, drill, and jigsaw, a cheap miter box with a hand saw, and some hand tools.  If you have a table saw and a miter saw, it would probably be a lot nicer.  But, I think it looks good enough to be in my apartment.

I had a lot of trouble with the luan warping.  On the sides and back, this just meant I had to nail it with lots of small finishing nails at pretty closely spaced intervals.  On the door, I had to be careful to make the pine frame rigid and straight enough to keep the luan flat.  It didn't work perfectly, the door ended up a bit twisted, but it was flexible enough that when the door is closed and latched, it pulls flat.

The door is held on with basic strap hinges, and I used a relatively strong latch to pull it tightly closed.  The door area is insulated with foam rubber weather strip.  I may double up on the weather strip for a better seal, but I am worried about using too much and having the door not pull securely closed against the seal.

The inside is lined with 1-1/2" pink foamboard.  I needed one 4x8 sheet to do the inside, but it wasn't quite enough to do the door, so I also used part of a 4x8 sheet of the cheaper 3/4" pink foamboard stacked in 2 layers to insulate the door. The insulation is taped up with aluminum tape, found in the same aisle as the insulation - I don't know if this was really necessary all over, as in many places the foam fit pretty tightly, but the roll was only 3 bucks and I figured I might as well do all the seams while I was at it.

The fan goes in the back right - there's a hole cut out from the plywood with a jigsaw, and the foam is carved away a bit for air flow.  There are 1" holes drilled in the other corners for return air flow, with one hole in each of the closer corners and three holes in the furthest corner, to try to get most of the air flow to be across the entire chamber instead of a small loop.  I also added a strip of cardboard so that the air from the fan has to go all the way to the top of the chamber and cascade down over the fermenter.  I noticed some severe temperature stratification previously, but it seems a lot better now.

Overall, I'm quite happy with it.  It served me well throughout the summer, holding temps in the mid-to-low 60's.  I never tried going down into the 50's, I suspect it would take a lot of ice changes.  Changing the ice does get somewhat annoying, but it's not so bad once it becomes routine - especially when roommates help out with it also.