I've only made a couple of bed sized quilts and that was years ago. For a long time I just didn't have the space to make them. Now I have the space but not the inclination. I think because of space limitations in the past I feel most comfortable making wall quilts no wider than 4 feet. I do all of the quilting by hand so it takes forever to make a quilt even that size. I think I'd get too bored working on something bigger because it would take forever.
I do a lot of applique and started off making single squares of simple patterns until I felt comfortable doing larger pieces. Something 10 or 12 inches square is a great place to start and they can be quilted and bound to be hung on the wall. I made a few when I was in my teens and my mom framed them under glass. They still look great 40 years later.