As a builder, we had a problem with a designer who made repeated mistakes. We contacted the company owner and simply said, we are way too busy to keep stopping projects and losing money on plan errors by a draftsman, how can we obtain rights to the design that we can use to build indefinitely. We were entitled to a "print" or set of prints in PDF form, but not the actual native design files. The owner was very understanding due to the amount of money we had lost in repairs and downtime, so he allowed us to purchase and release indefinitely the design of the townhomes for two thousand and change. We were then able to hire another draftsman to take those designs and tweak what we needed to then produce them in a production format for us. Unless you have a unique contract of some kind I would simply say listen I own the rights tot he design you can take it, unless it is like a homeowner that hired you to design their dream home, I think that situation might be different.