I made my own large scale swamp cooler based very loosely on figjams unicooler. I made a box out of 1x2 lumber and lined it with plastic shower surround material then caulked the inside. Cut a hole on one side for the fan and cut a hole on the other side for the pad (air intake)
I think one place where figjam is just flat out wrong is that he uses too large of a pump. The entire premise of a swamp cooler is that the Ideal Gas Law states that as the phase change occurs and the gas expands, the temperature of the gas is lowered, however for this to happen you want rapid evaporation. If the pad is too wet, it will interfere with evaporation due to cooling the pad itself.
Based on how big of a space you need you probably will need a pretty heavy duty fan.
I chose the Endless Breeze that has been discussed endlessly (haha!) for oversized swamp coolers (2.6 amps for 920cfm): https://www.amazon.com/Fan-Tastic-01100WH-Endless-Breeze-Stand/dp/B0000AY2Z6
Also, this one is a new one that I don't know how effective it is but moves a good amount of more air (2.8 amps for 1700): https://www.amazon.com/gp/product/B01JI0KOWG/ref=oh_aui_detailpage_o01_s01?ie=UTF8&psc=1