Step 1: Selecting the dimensions
Fortunately the Desert domes http://www.desertdomes.com/ site has a handy calculator to work out the size and type for any size of dome you need.
I elected to make a 9 foot wide 3 V dome this would stand on a 3 foot high sub frame to give the necessary height I needed.
Desert domes gave me the necessary dimensions for the 3 different length struts.
Step 2: The joints
A small hole was drilled vertically through each strut and a nail allowed the fixing of the elastic band. The bands were cut from an old bike inner tube.