We did exactly what you described last year, it was a DIY and very inexpensive which is what we needed at the time. It's working out well so far and way more shelf space than we need. Our pantry is 10x5. Shelves are 2x12" boards (which are really about 11 1/4" deep) and brackets are from amazon. The brackets hold 80 lbs each and we have 4 for each long shelf secured into studs so no worries on weight capacity. The last pic below is from underneath and also the shelves are stained in that picture. We are planning to add a cabinet with drawers at the far end. I don't have any photos of it completed with food in it but I can take some later when I'm home.
Q
Pull out for dog food counter
Q