I draft my patterns without seam allowance to start, then add it after I'm sure I've got the pattern right. Here's an easy way to add seam allowances to an existing pattern piece in CorelDRAW. I did this using the software at TechShop Menlo Park
Step 1: Start with One Object Outline
Work with one pattern piece at a time. If all your pieces are on one page, do each of them one by one. Each pattern piece should be one object with a single unified outline, rather than just a collection of lines or objects. If your pattern piece is a bunch of connected objects, use the Create Boundary icon to create a new object that has the same exact outline as your connected objects. Move it to the side, delete the original collection of objects, then move your new object back into place. You're ready to begin!