I followed along with the video series for the first 12 episodes or so and was able to run everything. I've continued watching (but not coding along) and now want to run the code of episode 30. I tried overwriting the handmade directory from the .zip file and running build.bat from the console command, but get the following error: 'cl' is not recognized as an internal or external command, operable program or batch file.'

I tried with episode 29 and got the same result. Am I missing something?

You need to run shell.bat first. After that you can run build.bat.