The idea of using a slope as a site for a compost bin is pretty practical. Compost needs good drainage, which the slope will provide, and often people are at a loss for ideas for what to do with a slope in their yard. If you are fortunate to have a south-facing slope, your compost pile will probably do well, but any site can work to some degree. You should try to build the compost bin level, or it might look haphazard and not attractive. This is a simple explanation for assembling a compost bin. You can get much more complicated if you wish.
Cut the landscape ties in half with a chain saw or hand saw to make 20 4-foot sections of timber. They will be stacked alternately on top of each other to form a bin for the compost. Keep them the same length so that over the years, when you disassemble the bin, you won't have to worry about which section goes where when it is put back together.
Lay down any two of the sections of landscape ties parallel to each other about 3 1/2 feet from each other so that they are going down the slope. Place another piece under both of them in the front, perpendicular to the sides. If the sides look like they are close to being level, check with the actual level to see how close they are.
Lay the level on the top of the side section. Lift the lower end of the level up until is it level. The space from the end of it down to the landscape tie will show how much you still have to lift the front of the bin. A 2- to 4-inch space can be filled with a few bricks set under the front cross piece of landscape tie. Smaller gaps can be fixed by sinking the bricks into the ground and then leveling. A steep slope might require placing two cinder-blocks under each end of the front cross section, to raise it enough to be level.
Set down two landscape-tie sections, one in the front and one in the back, after you have the bottom ones leveled. Continue stacking two more on either side and then the front and back again, until all the sections are used. The weight of the landscape ties will hold this type of compost bin in place, but since there is no hardware holding it together, you can easily disassemble it to remove the composted soil when it is finished.