Mine was made by my cabinet line, but another source for custom hoods that may be more reasonable would be your local steel fabricator.
I sent my teenage daughter to pick up a custom chase cover for a fireplace and when she got back she was in awe over all of the range hoods that were being fabricated.
It's just a thought for another source.
Good Luck.

Debra, what you want to hunt for is a 'range hood insert'. These are the fans that are made to be "dropped" or built into a frame you provide yourself. You can also purchase liners separately, which are metal flanges made to line the inside of the hood around the fan in order to pass fire safety code.

We are making our own range hood, too (can't decide if we're going to do wood, tile or copper). I bought my 40" insert from an online discounter - there are lots of places to look, including eBay, Overstock, Graveyardmall, etc.

Linked are the offerings from AJMadison, just because they're the easiest site to search:

Here is a link that might be useful: Range Hood Inserts

Whoops, sorry, just re-read your post and you're looking more for design insights on the hood surround itself.

We're tackling ours with our experienced carpenter friend next weekend, so I can be in touch if you'd like details?

We're planning to build and mount a 2x2 or 2x4 and plywood frame no matter which exterior covering we choose -- sheet copper, trim wood or cement board for tiling. (Lately we've considered zinc since we made our own countertops out of copper and don't want copper overload).

If you google search the GardenWeb forums as a whole, you'll find a number of threads with more details.

Here's one such thread.

This could be an interesting project, so long as you don't assume that you will save very much. However, for the result to be effective as well as aesthetic, certain requirements apply. You can learn a lot about these requirements from web searches and visiting the Commercial kitchen hood sites.

It would be unwise to start this project without knowing what the requirements are for function and design, including safety requirements.

The two functional requirements are capture and containment. Capture is getting the rising and expanding effluent into the hood (requires overhang of the cooking zones). Containment is keeping the effluent from getting back into the room. This depends on air flow and internal hood design, choice of filtering, etc.

Another requirement is fire resistance. The design has to be inflammable, and has to minimally grease up beyond the filters. This requires an air velocity in the stack of more than 1000 feet/minute.

Your building inspector may have opinions about what he will approve, so he should be consulted after you have a design.

kas

circuspeanut, I'm looking for any and all info on this project. Those links are helpful. I would be interested in hearing more about your hood.

OK, so I need to buy a range hood insert and a liner. Then build a frame to cover it. Sound right?

Kaseki, you are right as there is alot to think about and this might not result in a cost savings. Need to plan this out...

I just don't understand why these range hoods are so expensive. For our needs just a basic ducted fan would be fine. We have a 30" electric range and just do basic cooking.

We could just run the duct through a cabinet but it seems like a waste of a cabinet but that would the cheapest option.

All ideas are welcome.