What is the value in mining cryptocurrency?

What are some cryptocurrencies that are currently valuable as a mining prospect, and what is the most cost effective setup for building a mining rig? What are the costs involved as far as drain on the electricity, and what kind of return would you find out of any given crypto you're mining? Is it possible to build your own rig?

Anyone who currently mines who is on my friends list if you have any info to give I would be happy to know. I'm very curious about mining as a viable prospect. What have your experiences been?