Building with Rock

I own a newly built home, and they left a whole lot of rock, pushed to the back edges of my lot by a bulldozer. These pieces are mostly flat, ranging from small chunks to 1'x1'x3" pieces. Since I can't cart this off easily, and since I also need a storage shed/workshop, I was toying with the idea of using the rock as building material for the shed. My only experience with masonry is my combination mailbox/flowerbox I built from old brick. It didn't turn out too bad, and I learned a lot from the experience. So, what is the best way to build shed walls using rock? Must I lay the rock flat? Or can I stand the rocks on end and make it two rocks thick? Seems like I've seen it done both ways in professionally built buildings. Can I use the same premixed mortar I used for the brick mailbox? Thanks in advance for any help y'all can give. Robert Sewell