I had a similar situation in my last house. An electric oven w/ pull out tray below & a tall storage area above. I didn't use it for much food storage. Stored pots & pans below & tall things like my vintage Hamilton Beach malt mixer & the KA mixer above. Also, the bags of chips went up there.

That said, I never noticed any excess heat, particularly not below (heat rises). When you think about it, built in ovens usually go into wood cabinets so they must be quite well insulated so I wouldn't have any qualms about storing food there.

Want to add that storage above the oven wasn't what I'd call easily accessible. Least ways, not unless you're quite tall. I'm 5'5'' & have a long reach--monkey arms! Personally, I would plan to store bulky, seldom used items up there or do a divided storage for cookie sheets, etc. Remember that the cabinet is going to be counter depth, approx. 24''. I remember grabbing a long wooden spoon to reach in & give a bag of chips a flip out of the cab & catching them before they hit the floor...that was often easier than dragging a step stool

I echo ci_lantro - no noticeable heat problems, above or below our big (30") Miele wall oven. Directly above the oven we keep some accessible overstock of salad dressings and sauces and such, on a large (24") rev a shelf lazy susan -- or else as ci_lantro said, we'd never be able to reach anything near the back. And above that on the top shelf is the overstock of gallon jugs of vinegar and bags of rice and stuff -- ONLY accessible with a stepping stool (we had to give up our pantry in our reno, and this was one of the ways to get space for the Costco-size stuff). It's obviously far less convenient than a walk-in pantry, but if we plan what goes up there we don't need to access it much except to refill every-day use containers for rice, etc. Bottom line though, no heat problems.

My mother has stored her flours and oil over an oven since before ovens were as well insulated as they are now. I've checked my own ovens for heat spillage and the only one that's even a little bit of an issue is the warming drawer. If you have decent quality cabinetry the oven and food items shouldn't play together at all. They should ignore each other. Do check, however! Roast something at high heat for at least an hour and feel the areas above and below. If there's any added warmth at all, add some insulation.

I don't know why the area above a waist high, small single oven wouldn't be accessible, at least in the front on the first shelf or two. You'll have to measure it out, but I've never had any trouble, even when I was a lot shorter (tween).

In my previous cabinet oven combos, I've always stored seasonal items, like Christmas cookie cutters, Thanksgiving platters, etc in the upper shelving. I'll probably do so again. If I have space, I'm hoping to store my extra rolls of paper towels & paper napkins on the lowest shelves above the oven. I'm short, 5'2", so I like to keep every day stuff within my reach. In my (I hope) final kitchen plan, this cabinet will have the drawers to 36" from the floor, the 24" x 24" single oven, and shelves, so the shelves should begin at 5 feet.

I'm glad to hear that you don't think it's an issue, but I'll definitely take plllog's advice and roast something first to check on the heat before settling on the final location for the food. I was hoping the oven would get installed today, but it didn't.