Clock kit first - Build the case second
It is important to order the clock kit before building the clock case. If the case is built before getting the Mechanical Clock Kit it is possible the kit will not fit.
Why order first
It is possible to have a difficultly finding or adapting a clock movement kit to the current case built. The ideal dial size or other things would wanted but these items may not exist in the size needed for the case. Measurements that need to be correct for the clock kit to fit into the case. Order the Mechanical Clock Kit before building the case. With the kit set up on a stand while working on the case it can be measured. The various items on the kit such as the pendulum swing and dial size is known exactly.
What is not available
Clockworks.com offers a large variety of clock movements so this is the most easy thing to get. However when it comes to some components the resources can get slim on specific requests. Clock dials are the hardest part because there are so many shapes sizes and options. Such as round, square, hump top with no moon, hump with moon. Then you have all sorts of sizes, many of the antique clocks had clock dials that are in a size that is just not made on the market anymore. The grandfather clocks back in the day had over sized Clock dials with ships on them, cant get those anymore, as well as many other ones. Also you have to wind most clocks (unless they are chain driven) through the dial with a key. In other words the dial needs to be drilled out for the specific movement you ordered.
It is wise to get the Mechanical Clock Kit before building the clock case. Besides it will give an opportunity to set the movement kit up in your work shop to look at, get used too it, and measure for yourself what is needed.