A kit starts out looking something like this photograph from the Hubbard website. (The kit shown in the photo is for a French double, not a Flemish single, but you get the idea.)

I attended a workshop in Boston where instrument maker Mike Collins provided expert instruction on how to get started.  At the workshop, he helped us students assemble the case and install the wrestplank (where the tuning pins go) and a few other things. After the workshop, it was shipped to my home, and my harpsichord looked like this:

Here are the upper frames being glued in.  They help support the case against the tension of the strings, which will total about 104 N (about a ton!)

Here it is with all the braces glued in, and the boudin (reinforcement for the soundboard) in place.

Wood swells as it absorbs moisture from the air. These data are for two different pieces of Sitka spruce, measured along the radial direction. The pieces were supposed to be cut from the same piece of wood, but as you can see they have quite different expansion coefficients.

The soundboard must be installed with an intermediate moisture content, so that it does not shrink too much and split in the winter, or swell and buckle from the humidity in the summer. To learn how long it would take for the soundboard to reach the desired moisture content, I performed an experiment to measure the equilibration time constant for a response to a change in the ambient humidity (my result was 14±3 hours for 1/8" thick quarter-sawed Sitka spruce for an increase in humidity).

I spent some time trying to make a pewter rose to go in the soundboard hole, but in the end I decided to buy one made in parchment by Elena Dal Cortivo.

Here I am gluing in the soundboard.

To get a nice finish on the case and stand, I painted five or more coats, which I then rubbed down with several grits of sandpaper and polishing powders, and finished off with linseed oil. The soundboard is coated with thinned shellac. (Later, I'll be adding gold leaf highlights.)

Of course, I had to measure the response function of the soundboard -- because I can. Here is a sample response curve (how much vibration you get for a given degree of excitation), showing how the soundboard responds at low frequencies with the rose hole open (blue) and closed (red).

Finally, the instrument has to be strung, the keyboard assembled and installed, and the jacks and plectra individually adjusted. Here are some pictures of the final result: The motto, ἄειδε θεὰ, is from the opening line of the Iliad. It says, "Sing, goddess."

The physics of the harpsichord is quite interesting.  Check out "The Acoustics of the Harpsichord," E. L. Kottick, K. D. Marshall and T. J. Hendrickson, Sci. Am., Feb. 1991, p. 110.