Making dirt jumps and pump tracks

I have been trying to make some dirt jumps and pump tracks a lot. I seem to run into a problem when making them though. When I make rollers it doesnt really seem like they work. I'm not sure if my rollers are too sharp and almost have a lip, too mellow or improperly spaced. How do I fix this? When I have been making dirt jumps, I can never make the lip correct. The lip is smooth and pretty sharp, but when I jump it, the lip kind of throws me off balance in the air, is it too sharp? How do I make a good lip and a good slope of the jump's surface? Also, how do I gauge where to put the landing? Am I better off to start with a table top?