When you sew quilt blocks using a foundation fabric to piece onto, you are usually instructed to cut the foundation larger than needed to allow for shrinkage.  The same is true for patchwork for clothing that is created on a foundation.  I cut my garment foundation pieces about 1/2" larger all around than the pattern pieces I will use.  I create the patchwork for each piece, then trim to size using the pattern.  Foundation fabric can be batiste, muslin, well-washed flannel, or even a soft batting (my favorite is Quilters Request Cotton).