Hello
I am an OS X and Windows system developer with over 7 years of experience.
During this time I have worked with various frameworks for Mac, from high level Cocoa UI development to low level system daemons and kernel extensions programming.
I do have Windows/Visual studio development experience (in C++) as well, and created quite large projects using VS and Xcode (on of the projects is a Parental Control system, which involved Windows and OS X network filter kernel development and a native Cocoa+WTL UI application-front end).
I use multiple design patters in my applications, as Cocoa itself is a pattern-oriented framework.
I also have scripting experience. I heavily used AppleScript for automating Mac applications (for example, one of the projects was controlling Microsoft Word from another application using AppleScript). I use bash scripting for automating development tasks, like building the product including automatic building of an installer package for mac and a DMG package in one click.
For what it's worth I have built Qt applications (mostly using QtCreator, although I had projects that the customers explicitly asked to be built in Xcode), I do have my own "pet project" written in Qt.
Would be happy to help you with your project.