"where should I put it?"
Most of us just want to get through with the chore of cleaning out stalls and move on to riding the horse. So the closest place is usually out the main barn door and as far as you want to walk (which from viewing piles, isn't that far). That isn't a problem when you have it regularly hauled off or spread later. There are though, some things that should enter your thoughts as you pick your spot. We , more often than not, see piles with the gutter or drainage running right by or into the pile. This makes the manure heavier and more attractive to flies. The lighter the pile the more we fit into our trucks without hitting our weight limit. The less moisture in the pile creates a less attractive spot for flies.
This barn has, in my opinion, a great set-up. If you have space and a hill. By digging into the slope one can empty a wheelbarrow or small dump trailer over the edge with out use of a tractor to push up and contain the spread. Moisture can also continue down the hill and stop the decaying process, that will draw in more flies.
This pile is off to the side in a lower spot in relation to the barn. Further to the left of the fence is a slope. It has ease of use for the owner. With regular pick up, the fly population can be kept down.
This box (to the left and below) is one of the sturdiest that I have seen yet. It is 12x8x10 and has solid phone pole corners with a dado style joint for the 2x6 walls. The rails on the ground are genius. These are galvanized poles ( old well pipe would work as well). The poles will help with accidential digging out of the floor. Make sure to have a length that goes from the back wall to 2-3 feet beyond the opening of the box.