About the wood and wood size
This project call for 1×6 (150mm x 25mm) actual size and 2×4 (100mm x 50mm) actual size wood – which is usually a rough wood
(not dressed, planed, or dimensioned). It will give a bit of a rustic look and be inexpensive. Treated pine would do.
Would the rough wood pose problems splinter wise?
Not really. The fur (for lack of a better term) on the treated pine is soft and if need be, it wouldn’t take much to sand the parts that matter.
In USA you can get 1 in. x 6 in. boards easy enough (smooth or rough).
In Australia you can get 150mm x 25mm treated (rough sawn) pine commonly used as plinth board.
In NZ you can get 150mm x 25mm treated fence paling (rough sawn).
In most other countries you should be able to source 1×6 (150mm x 25mm) wood without too much bother
in some form or other.
Altogether you will need
Allowing for a little bit of wastage…
• 12 ft (3.6m) of treated 2×4 (100mm x 50mm) actual size lumber.
• 72ft (22m) of treated 1×6 (150mm x 25mm) actual size lumber.
Note: treated 1×6 (150mm x 25mm) and 2×4 (100mm x 50mm) actual size lumber usually means (rough) lumber before it has been dressed (surfaces, planed smooth).
When purchasing lumber try to get as long a lengths as possible to minimize waste.
You will also need…
80 of 2″ (50mm) wood screws,
48 of 3″ (75mm) wood screws,
and some glue.