Just walk up and down your marquee. A roof 40ft x 20ft would take about 10 mins a side. You can see the clean marquees hanging up in the back ground. I used to do 4 roofs a day which took about an hour including folding the dry tents, scrubbing and handing up the next set to dry. In a week 20 roofs, over the winter (about 30 weeks my stock of 600 or so panels) Then the trick is to was the worst 4 roofs each day on a rolling program.