Welcome to the Marine Depot Forums.

I would assume if you do a google search for: DIY plans protein skimmer that it should come up with some plans for you.  IF you are handy with acrylic and are very use to working with it, this certainly can be a money saver.  If you have never worked with acrylic it may not be as easy as it looks.  I have seen many people who built their own skimmers and eventually bought a premade one because they could never seem to get theirs to work right.

For your returns, bascially you are looking to get good flow throughout the tank avoiding dead spots.  This can be accomplished many different ways, whether it is returns on the bottom, top, sides, etc...  If you are trying to avoid using powerheads in the tank, putting the returns towards the bottom certainly can help with this.  BUT IMO returns on the bottom should come from a closed loop and not your return pump.  In the event you lose power, water will siphon down these returns and could potentially drain the tank and overflow your sump.  Even if you use a check valve on these lines, there is still a very good chance water will still backflow down these lines.  So for a return line, I would say keep those towards the top.  For a closed loop, you can put them almost anywhere.

Random flow is generally better than the flow from one direction all the time.

As long as the flow is not to high you can point it at the rock.  If the flow is very high, I wouldn't point it right at the rock.

HTH,

________________________________________________

Keith

“I'm hitting the woods just great,
but I'm having a terrible time getting out of them.” - Harry Tofcano