Chris, are you planning to buy factory-built cabs or from a custom-builder (or DIY)? You or a true custom cabinetmaker can build whatever you like, but stock factory cabs typically come in 3" width increments: 24", 27", 30", 33", etc. I just googled and picked a couple of random wall ovens, and they both specified cabinet widths equal to their nominal widths, i.e. a 30" oven uses a 30" cabinet, etc.

We'll be having them custom built. I guess my question boils down to this--is there space required between cabinets, and if so, how much? Or does the cabinet specification (eg 30" cabinet for 30" oven) include the space between it and an adjacent cabinet? Not knowing how cabinets are built, I guess I just don't know how the "hook together" etc. So back to my example, will the 27" oven next to the 36" cooktop eat up 63" of wall space, or more?

Thanks,
Chris

If I were you, I'd try to find a Kitchen and Bath Design software program where you can enter the specifics and it calculates the actual dimensions. A 30" cab is 30", but a cabinet for a 30" wall oven would not be 30". Depending on how it's framed it may be much larger. Is your cabinet maker walking you through the layout with appliance specs in hand? We got some help from our custom cab guy, but that did only so much good. There were a few mistakes that could have been easily corrected beforehand if we'd had access to the software he was using.

'a cabinet for a 30" wall oven would not be 30"'

From what I can see looking up spec sheets, this is not typically true. The minimum width cabinet specified for the 27" wall ovens I saw was 27". That's because, while the visible part of the oven is only slightly less than 27" wide, the back of the unit is substantially smaller so it can slide between the sides of a 27" cabinet. If you wanted to put the unit in a larger cabinet then you could do that, but it would be an entirely aesthetic choice.

For your purposes, I'd assume that your 36" cooktop will require 36" of space, a 27" oven will require 27" of space, and leave it at that. Refrigerators can be a different story, as they require clearance space for the doors to open sideways, as can apron-front sinks which are sometimes installed with cabinet stiles coming up around the bowl.

Here is a link that might be useful: Look at the weights and dimensions part of theses specs

The 27" oven I'm interested in requires a 25.5" cutout. Say there are 2" stiles on the sides of the cabinet, then the cabinet would have to be 29.5" total width, correct? But wait (thinking out loud here), I guess that the cutout part would cut into the stiles, so that the actual width would be the cutout plus the width of the sides of the cabinet, 0.75" each, so that's 27". Hmm. Is that thinking correct?

The other consideration, I think, is that the oven cabinet (full height) will have to be its own unit, since it will sit next to a counter-height cabinet. So we'll be doubling up on the sides between those two pieces, right?

Draw the doors and the appliances as you would like them and let the cabinet maker decide how to frame it all out.