Circular window method

Any odd shaped window/door opening you have to use custom modeling. Create a wall opening that is slightly wider than your shape. Measurements & guidelines are important. Create the custom wall, draw shape using custom tools. For circle: create a square w/guidelines, then draw guideline that equally divides each side. Where the guidelines meet in the middle-start your circle using circular tool. Delete the inside of the circle, extrude to the depth of the wall. Group together & save. In design interface click model & move in place.