I AM TRYING TO BUILD A FEW CONCRETE STEPS. WHERE WOULD I FIND INFORMATION ABOUT HOW TO FIGURE HOM MUCH CEMENT I NEED ( WHAT KIND OF CEMENT SHOULD I USE PLASTIC CEMENT OR PORTLAND CEMENT) WHAT IS THE RATIO OF CEMENT GRAVAL AND SAND. I WANT TO HAVE A 7" RISER AND 4' WIDTH 2' LENGTH.