Here's a parts list for you to reference if we're not able to build your bike for you. There's lots of options of course, but this is a good way to do it. It's not that different than a regular bike except you'll need two handle bars, tandem specific cranks (we got em), a stoker stem (we have one), tandem specific wheels, and four(!) chains. Call us with questions!
There are also incidentals like brake and shift housing and cables. We suggest getting those from your local shop, but we have 'em on the site too. Actually, make sure to get a couple things from your local shop.
Thanks for getting a frame!