I built my keezer last fall(ish).
I went with 2x8 lumber for the main part of the collar to give me plenty of space for kegs (I have two 6 gallon kegs, so needed more height). You could go with 2x6 or maybe even 2x4 for the main part.
I then used some hardwood to 'skin' the front and both sides. I left the back mostly bare (for the hardwood) since it won't be seen at all. I did go with enough hardwood to mount my drip trays to that.
I used a couple of leftover pieces of the hardwood on the back of the collar to keep it from slipping forward (in a worst case scenario).
The lid got transplanted to the collar for the hinges.
The power feed for the LED in the lid was long enough to not modify it (other than remove the screws holding it in place to allow it to expand enough).
I had some taps and shanks already (three taps and shanks) but added three more stout taps to the setup.
Used stainless gas bulkheads to pass through the collar (left side, back corner) to make it easier to change things later, or disconnect when moving.
I have a dual body CO2 regulator passing through, fed by a 20# CO2 tank. Plus a small nitro/CO2 mix bottle with it's own regulator. It made a ton more sense (to me at least) to keep these outside the keezer. For one thing, the 20# CO2 tank isn't light (even though aluminum). For another thing, the gauges read accurate (high pressure side especially) when NOT in the keezer (chilled). Not to mention it's more room for beer kegs.
I can fit 8 kegs on the main part (10.? cubic foot freezer) and two more 3 gallon kegs on the hump (or cans).
With the collar, you can set it up to do this type of thing easily. Where you otherwise won't have room for additional kegs on the hump.
Yes, it's not exactly easy to get the 6 gallon keg into the keezer, but that's only in one direction. Once it's empty, it's easy to remove.
I'm using two of these drip trays:
Amazon.com: Kegco SEWM-127 Drip tray, 12" x 7", Stainless Steel: Kitchen & Dining
It makes cleaning them easier since I can remove either one without trouble. Clean it, then slip it back on.
Putting taps through the lid isn't viable for me since it's going against a wall and I need to fully open the lid. Plus, you would need to chill the tower if you did that. Not really an issue with a collar.
I did pick up a fan (computer style, running off of 120v) to keep the air moving inside the keezer. It has a speed controller as part of the setup. Works well.
With lumber prices being all over the place (or at least higher than when I did my project) you'll need to price it out in your area. I made sure to get enough of the main body (2x8) to do the job plus the hardwood to skin that. I just wish I had better wood working tools here. Putting the holes in the front was the hardest part. Mostly because I wanted them true. So I used my floor drill press. Doing that alone was interesting.
