Screw together the four shorter beams, using L-brackets to secure the connections, to make a rectangular base that is 4 inches tall and 30 by 12 inches in area. You can adjust these dimensions however you like to suit your personal needs.
Screw the four 1-by-2 beams upright onto the base, using L-brackets to secure the connections. These four beams will form the upright frame of the pantry. Orient the beams so that they are coincidental with the outer corners of the base, with the longer sides running in the 12-inch direction. The rectangular space between them will be 28 inches long and 8 inches deep.
Nail a sheet of 12-by-28 wood directly onto the base, in between the wall beams. Notice how the sheet just barely fits. This will be the bottom shelf of your pantry.
Screw L-brackets into the wall beams at 11 inches up from the bottom of the beams. Make sure they are level with one another. This will create a support for you to install the second shelf. Do so, and then secure the shelf with nails through the wall beams.
Repeat this procedure for the remaining four shelves, with the top shelf being all the way at the top of the 66-inch wall beams. Adjust the shelf heights, and the wall beam heights, however you like.
Nail one thin wood sheet to each side of all the shelves, forming retaining walls that will prevent your stored goods from falling out of the pantry when it rolls.
Turn the pantry onto its side and screw the four caster wheels into the base beams at the bottom. Do this on the outer corners for maximum stability.