Most 9" blocks (really, 9 1/2" before being sewn together) are some type of 9-patch block made up of 3" units. Simply change the finished size of these units to 4" to get a 12" block (12 1/2" before being sewn together with other blocks)
Most 16" blocks (really, 16 1/2" before being sewn with other blocks) are some type of 16-patch block made up ofr 4" units. Simply change the finished size of these units to 3" to get a 12" block (12 1/2" before being sewn together with other blocks)
Try looking at various quilt blocks, regardless of size, and see if you can spot if they're a 9-patch or a 16-patch. Doing so will help you be able to draft patterns in the future. You can use the blocks at Quilters' Cache for practice.