According to hhmi:
Students use paper nucleotides printed on card stock to build a single-stranded DNA sequence assigned by their instructor. They then use the rules of base complementarity to construct a second strand and generate a three-dimensional double helix. Through building and observing this model, students explore the basic structure of phosphodiester bonds, base pairs, the spatial relationships among the components of nucleotides in DNA, and the antiparallel nature of the double helix. Written and video instructions describe each step of the model-building process.
Get the activity here.