It's going to be sized to the range and space available of course but since you are building the box for it, one discussion that I would have with your GC is to make sure the finished box takes full tiles in each dimension. I (If you are doing running bond you will have some cut tiles or have to use a line that has 3x3 as well as 3x6) --but you should be able to come up with an appropriately-sized hood that has Minimal cut tiles

I found this picture by lavender lass but it doesn't really sound like this is what your looking for.

For what it's worth, Mtn, here's mine, altho I'm sure you've seen it before:

As you can see, the cabinets predated the hood so I had little wiggle room to exactly space my tile (3x6); in the end it's not all that important, as long as you let whatever size cuts you wind up with take up the same width on both sides.

I LOVED this hood and recommend tiling the underside, too -- it was so easy to clean inside and out with a damp sponge. I'll be recreating it in my new kitchen in some form or another.

And in white, one of my inspiration pics:

Ineffable,
Yes, of course, the quixotic quest for a world with not tile cuts! : )

Romy, thanks. I know I saw it somewhere but the only one if can find is the one you found.

Circus, I always love to see your kitchen anyway. And thanks for the inspiration photo, too. And .... new kitchen?