Rat guard serves two purposes; provides a shelf for the bottom edge of the metal siding to sit on and keeps pests from entering. I use it as a shelf for the siding. Here is a close-up picture:View attachment 589112
If building a metal sided building on a slab (either with post brackets or studs) you could also tack an extra piece of 2x on the top inside of the forms to leave a similar rabbet for the siding to overlap down into past the top edge of the slab to close off all the rib ends. Backfill the ribs on the inside with grout if desired.