10 inches wide and 1 inch longer than the length you want the shirt to be.
subtract 20 inches from your bust measurement and divide it by two to find the side panel width measurement. for example, if your bust is 36 inches subtract 20 inches to get 16 inches and divide to get 8 inches for each side panel width.
add 1 inch to the side panel width measurement and cut the stretchy fabric panels to that width. the length of these panels should also be 1 inch longer than you want the shirt to be.
lay out the fabric panels in order of the front panel, one side panel, the back 