Here's a neat idea I found over at Birding / Wild Birds (About.com) blog on how to make your own squirrel proof platform bird feeder using a piece of stovepipe. It looks like a very simple, but effective design. Although, the feeder will need to be placed in an open area of your yard so that the squirrels cant leap from nearby trees or any other structure - I would say at least least 10 feet. Here is a photo of the design (I hope they don't mind me referencing it...) --
If you’re looking for something a little more fancier, you can use this design as a starting point to create something bigger and better to your liking.
Here is a list of material and directions to complete this project: