nixrox, please do a bunch of homework before you build anything.
Hydraulic systems can be very unsafe and fail at the worst times. As you probably know it's why when working under a car you don't use just a floor jack, you lift with it then use jack stands to make sure the car doesn't come down on you.
I only mention this so you'll be safe and so if you build a lift you'll include whatever is necessary to be extra safe.
The last thing any of us want is for something really bad to happen to you.