There are a number of different approaches to planning a T-shirt quilt. They range from throwing all your T-shirts in a box, handing it off to anyone who says she can make a quilt and hoping for the best, to micromanaging the quilt down to the last stitch.
We would suggest you aim for something in the middle. We have a number of articles that can help you work through the entire process of planning your quilt.
We are always happy to help you with your quilt so, please don't hesitate to contact us.