I've also built a fermentation chiller. Large enough for two carboys. I never tried lagers, but if I changed ice every day and a half (about a gallon to a gallon and a half of water), I could easily handle mid-60s fermentation temperatures (house was at mid-80s...but the unit is well insulated).
In an effort to move along my desire for a kegging system (after more than a year, I may finally be there in a few weeks), I picked up a chest freezer and a temperature controller. Raised the lid, as others have done so I will be able to add taps. But, I also changed out the cooling system on my fermenter.
I keep both units side by side in our utility room. I added connectors to the muffin fans (I used two in my design because I had them) and now it cirulates air with the chest fridge. It builds up a lot of condensation in the fridge over time, but works well.
If somebody is really interested, I'll take some pictures, but it's really just the fermentation chiller (nearly 4' long, 2.5' deep) next to a chest freezer with two 2.5" plastic hoses between them. Inside the chiller is the standard two chamber design. Small for the ice, large for the fermenters. I just now have air hoses snaking through the small side to where the fans are located.
Jim