If you are going to make it stationary and you have a wall masonary or studded then you are home free with a simple but great design I use all the time for work benches.
OK here we go,
cut the top of the bench form 3/4 inch plywood to what ever size you need , 24 inches wide is usually plenty of room for the width ,now for the length,if you have the room keep it the eight foot in length it is.
Now take 2x4's and cut them so that they stand on end and go around the outside edge of your bench top,this gets hard to explain but if you are doing it right the top and the 2x4's are now 4 1/4" thick.
lift the plywood up and set the two short 2x4's on each end and then put the front 2x4 in place,line all three pieces up and attach with 1 1/2" coarse thread drywall screws.
you don't need to attach the back 2x4 yet because you are going to screw it to the wall or anchor it to the masonary at the hieght you desire your workbench,then you will lift the top into place and rest it on the 2x4 that is secured to the wall,thats when you will screw it to the plywood top of your work bench.
You will need to have a 2x4 handy to temp screw to the front of the bench to support the bench while you measure and cut the legs ,you will mount them under the bench to the inside box of the 2x4's that the top is already attached to,you will angle them back and they will rest against the wall where the wall meets the floor.
This project is quick and clean and easy to make.
For a really accurate top have the home depot guys cut the top with that panel saw they have and you will get a true enough 24 inch work bench top.