Check out these DIY pieces of gym equipment:

Squat Stands with multi-level catches.

Dumbbell Rack (multi-functional: EZ Curl Bar holder, Weight Plates holder, Situp bar.)

They're all made of wood and are easy to assemble.

Homemade Parallel Grip Pull Bar

This homemade Parallel Grip Pull Bar is inexpensive to assemble. It's made of steel and best of all, there's NO DRILLING and NO WELDING required!
With a parallel grip, you can minimize stress on the wrists and forearms while stacking up the plates on exercises like Pull-ups, T-bar Rows and more. You can even build a small, handier one to bring to your gym if it doesn't have one.

If you're interested in self-spotting squat racks that are made of metal and easy to build, check out this link:
homemade safety squat racks

Here's the homemade dip station I have at home - multi-purpose too.