How to build a REAL locomotive?

how to build a REAL locomotive not a model train. I was thinking of making a small but operating real life locomotive for myselff. NOT G scale but the same size of some of the small locomotives on the rail today.
how to build a small shunting/switcher type locomotive out of stuff u can get from a junkyard?
i am thinking of building a single locomotive to run in my family small backyard out of JUNK. not the stuff they actually uses.

again I WANT TO BUILD ONE OUT OF JUNK FROM A JUNK YARD