DISCLAIMER #1 – On the history of design, consider me an “internet expert”.
Lots of googling suggests that Liberty & Co retailed versions of various Theban stools from the late 1880s into the 1920s. Swiss and then Danish designers started around 1900 and carried on through the 1950s. I’ve dumped some of my auction site and lifestyle aggregator screen grabs into this image and will limit myself to a few general comments…

These stools follow the basic form of the Theban originals but weren’t intended to be exact copies. They would have required some hand work but were designed to exploit the efficiencies of machines found in production workshops from the late 1880s up to this day. The most common modification was to move the connection of the seat frame/leg joint down so the bottom surface of the wood block could serve as a reference face, making it simple to register a dowel drilling guide instead of cutting an oddly recessed mortise and tenon joint.

Now that we’re talking about particular bits of the construction, let’s quickly nail down our terms…

DISCLAIMER #2 – I won’t be providing any clean measured drawings, only napkin sketches.
So we’re ready to start marking out and cutting up wood. In the next instalment we’ll talk about tools and get the woodworking underway.