I have never bought all the fabric at the same time. I find a piece I love and buy a good amount. Then decide on what type of pattern it would look good in, then the fun part starts. Trips to the quilt stores. We have several really good quilt stores in our area and it is so much fun to take the day and drive from one to the other looking for fabric to complete the project. I always hope that the first store doesn't have all the fabric I need so I have an excuse to drive to the other ones.
This past weekend, my husband was showing off his steam locomotive in Prineville and I went to a lovely quilt store. The lady who owns it was so nice and she had wonderful fabric. I left with way too much fabric, but I had a great time.