my legs come way down does anyone build a set of blocks to put under jacks. someone told me it is unsafe because it could roll off. I am thinking of cutting 2x4x12" and make them about 8" tall
If you put blocks under the landing gear you don't want tall skinny blocks. Based on your measurements you will stack the 2X4s to create a stack 8" tall this is also referred to cribbing. I would not go much taller than 8" with a 12"X12" base.