Battens are simply long strips of wood. They are easy to make and handy to use during construction. Battens used in construction are similar to the battens used in sails, but the ones in sails are made out of much higher quality wood!
The battens used to hold the tar paper in place on the tiny house are made out of cheap pine 2x4s from Home Depot. A 2x4 is placed on a raised platform (scrap pieces of wood) and then ripped with a skillsaw.
A rip fence is installed in the front of the skillsaw, allowing you to control how wide you wish to make your cut (how thick the batten will be). I cut mine to 1/4" thickness. To cut the batten, the rip fence is placed on the side of the 2x4 and held firmly onto the wood as the cut progresses. The rip fence lets you take your focus away from how thick you are cutting and instead focus on holding the saw onto the wood. Cutting the battens is as simple as holding the saw and pushing it along the plank! Instead of buying pricey battens, buy a 2x4 for less than $2 and rip several battens out of it; because of losses by the kerf of the saw, I was only able to get 6 battens out of the 2x4. This would equate to $0.33 per batten, much cheaper than buying battens from the store.