Check the TAMU Agrilife Dallas Extension Center course calendar; they annually hold several rain barrel sessions around the east side of DFW - usually in conjunction with other organizations, so enrollments are not always open to everyone.

Edit: Here's their YouTube overview of the Agrilife Dallas Rain Barrel class.

We're in Dallas and have 3 rain "barrels" in our yard holding 935 gallons. Pretty simple really. Don't think you need a class. Ask me anything. lynnmariep at gmail dot com.

We have built our own also from the 275 gallon IBC containers and would be willing to answer questions.

There are lots of online sites with written and pictorial instruction. Do a search for "building rain barrel". There are also tons of videos on building rain barrels and connecting several together. See this YOUTUBE link.

Finding suitable barrels is perhaps the hardest part. Look for "food grade" barrels that preferably did not contain a strongly scented food ingredient. Do not use barrels that contained non-food products. Much easier to find are trash containers like THIS. 32-gal trash containers can be had for between $15 and $20. The larger 44-gal container can be much more expensive, but if you want to save a large amount of rain water you will spend less on connection hardware for multiple containers to get the same amount of water. Remember that due to ullage (space between overflow and the lid) a 32-gal container may only hold 30 gallons.