The family outhouse wasn't just thrown together willy-nilly. Oh, no. It was an object of pride. A showcase of engineering and ingenuity and a symbol of prosperity. There was a true science used in the construction of 'the throne'. 
It had to be built using only the best quality lumber. Generally, with 2" x 6" floor joist, cedar walls if possible but most likely just good white pine. Usually, the roof was just wood, but a fancy privy could have shingles and the la-ti-da privy might have had a tin roof. The roof slanted away from the side with the door towards the back to allow maximum rain roll-off. Also, you needed less height to sit on the crapper bench than you needed to drop your long-johns.
A standard structure was about 6 feet wide x 5 feet deep with the roof measuring approximately 8 feet tall at the highest point. Of course, those measurements would depend on whether it was your simple one-holer design or the more elaborate two-seater. A good coat of white paint would definitely set yours off from the neighbors and become the envy of the whole county. Don't make the door fit too tightly and remember to cut a crescent moon shape in it for proper ventilation and the only source of light.
A good supply of Montgomery Ward or Sears catalogs and a fly swatter were luxuries fit for the queen.

the important things 
will often go unnoticed—
until you need them