We've been using DCP-o-matic, which is free and has worked great for us. The first time we used it we got lucky and managed to test our DCP at our local small cinema before delivering to the festival. Saved us $6000 over 3 projects. Delivery requirements sometimes vary and, in our experience, we have always needed to deliver on a usb hard drive (with less than 1tb capacity, or you could format a larger drive to create a small enough partition). Preferably, nothing else should be on the drive and use NTFS drive format, although OS X Extended does seem to work. I'd really suggest to test your DIY DCP to avoid any last minute scares.