A couple of homemade trailer lift pics.

3" higher than stock

4" higher than stock

I prefer the extra bracing on the bottom one over the one above it but I think I would have added a piece of steel plate on the outside also. For myself if I wanted 4" of trailer lift I would go with the 2X3 blocks under the springs in the top pic and 1" longer shackles or the same blocks and build up the spring pack on the bottom for the other 1" of lift, it would be cheaper and a lot less fab work.