they are all different.

you might go talk to the manager of one near you.

Or just guess at the dimensions, since they are all different, who would know? or, pace out the outside dimensions, guess at the height, and go from there. take photos.

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Using Google Earth, the store in my neighborhood measures about 100 feet by 140 feet, and it has parking for 70 cars. I’d say it is 16 feet high, with the entry corner having a taller parapet feature, maybe 25 feet high.

If your model will include the whole site, there is a sidewalk all the way around the building, maybe 6 feet wide, a dumpster enclosure and a drive-thru portico.

Driveways are typically 24 feet wide and parking stalls are 9 feet wide by 20 feet long.

They come in all different sizes and shapes. The one near my house is about 130 feet square. In 1/4 inch to one foot scale, that would be 32-1/2 inches square, which is a pretty big model. You might want to make it a smaller scale.

At 1/8 inch to a foot, it would be 16-1/4 inches square, which is reasonably portable, and it’s close enough to HO scale that HO scale figures, furniture, and trees would work.

Small details would be getting hard to see, and hard to model, but you could make shelves and sales racks out of cardboard at that scale. If you have to build it at a larger scale, you can apply what modelers call “selective compression,” making the important areas larger and compressing less important areas, like stockrooms and storage into less of the space.

Have fun.