Draw a large semi-circle on a plywood board. Use a pencil, which is easier to erase if you make a mistake or miscalculation. The arc should be as large or small as you need the igloo to appear.
Draw an entrance tunnel on the front of the igloo, if this is the front of the igloo. If viewed from a 3/4-angle, the tunnel should extend, and then arc downward following the igloo's arc. If head on, the tunnel will appear as an arch at the front. If you plan to have actors climbing into the igloo, you will also need to mark an opening through which they can climb.
Create a brick-like pattern on the model of the igloo in pencil so you can correct errors. When satisfied with the appearance of the igloo, trace the pattern in marker.
Cut out the pattern of the igloo, and the cut-out for an entrance hole if there is one. Sand the wooden shape down to remove splinters and make it safer for actors working with the prop.
Paint the outlines of the individual bricks using a thin brush. Paint the bricks in white. Mix some black and white paint to make grey, and fill in some shadows to give the igloo a three-dimensional appearance.
Measure the height of your igloo. Cut a 2-by-4 plank to be two-thirds the height of the prop. For example, if it's a 6-foot igloo, this back brace should be 4 feet tall.
Make a floor brace that is one-quarter of the height of the model. If the igloo is 6-feet, the brace will be 1-1/2 feet long.
Attach the floor brace to the bottom of the back brace in an L shape, then tack the back brace to the back of the prop with the floor brace on the floor.
Measure the distance between the end of the floor brace and the top of the back brace. This should be the third side of a triangle. Cut a length of 2-by-4 to that length, and attach it to the model to create a strong backing for the model that will keep it upright.