Bevelling the trench from a narrow opening provides more sleep space and the smaller opening makes for less heat loss. If possible, cover the opening. Proper location for the snow shelter is important. Protection from any wind and level surface are both considerations. Rocks or trees can provide a break against the wind.
Conifer trees are particularly good.
If snow is deep enough, snow trenches and snow holes can take advantage of lower branches for extra shelter and support burrow underneath them. Yes, it is a great windbreak, but metal surfaces also suck up heat their insulation value is nil. Once the shelter is prepared, a fire should be the next priority. Dig out a small area for the fire, preferably with a shelf for sitting one may as well be comfortable. It should be deep enough that when a person is sitting, his or her head is out of the wind.