First off, I think this is a great idea, and from what I can see there are very few products like this on the market. I would love to talk to you more about the scope of the project. I do Mac OS X development as well as iOS development (I actually think this could make a great iPad app.)
If I were to design this as a Mac or iOS app I would utilize Apple's Core Data framework to persist a users projects in a database. The project database could store not only the pattern, but fields for title name, photos of the finished product, recommended hook size, yarn types, etc. To create the pattern the user could choose from a menu of stitch icons and colors, add the stitches to the screen, and then drag and drop stitches into position. I know it is common to crochet circular patterns so I could develop a template for such patterns to help keep the pattern aligned with user-defined circumferences. I could also develop functionality to select a set of stitches and repeat them as the user needed. And finally, I could integrate cloud services like iCloud or Dropbox for saving patterns, and social media api's to keep the users friends updated on current projects.
I would love to discuss your vision for the program and perhaps see examples of crochet chart formats that you would like to use (I've seen some slight variations in charts online.) And also examples of user interfaces that inspire you.