that is not complicated in the case you describe, just walking here and ther, when you feel confortable to build sothing here, just open the console and type:
player.getpos x
player.getpos y
player.getpos z
that way you have the 3 coords. You just have to create the "ref in the right cell, or create your own cell...
You can get the cell id by selecting anything , a tre, a rock (avoid the ground), and make a research about the formid you see up the console.
It is the old way, but it works.