Nistara Randhawa gave a presentation on writing your own R package. Unfortunately the audio malfunctioned on the livestream, but Nistara’s incredibly helpful post accompanying the presentation can be found at the link below. From Nistara:

Learn how to write and document your own packages using devtools and github. You’ll need git and rstudio installed on your laptops (the prerequisites listed on are useful for this), as well as the ‘devtools’ library

Nistara’s post on Writing your own R package.