Survival skill YouTube channel overthehill outdoors presents a step-by-step instructional video highlighting how to build an igloo from snow by oneself. In all, the building process–which occurred in the mountains of Utah–took around seven hours to complete.
The traditional method of igloo building adds the blocks in a continuous upward sloping spiral. That works well, especially if you have an assistant helping you. But when I’m working alone I prefer the concentric ring method shown in this video. I use the string when teaching first-timers to cut blocks at the correct angles, but once you’ve made a couple of igloos you’ll be able to eyeball the cuts just fine without it.