There are a lot of diy videos out there for anything you need, a little advice before starting find out your costing for all your DIY parts and compare with ready store bought product.
I think the over flow pipes is a great idea for someone not needing to drill.(I think I will building one for one of my tanks)
A DIY skimmer sure is due-able but I don't think for pennies.
Diy rocks, after all the work, tools and equipment needed it sure is cheaper to get
dry rocks and seed it with a couple lbs of live rock and voila ready for your tank.