Thanks for this course guys!
First HDA I make: Procedural Bookcases & Books
I have built user controls and user-controllable randomness for almost everything in the books and bookcase HDA. I also added a user-controllable parameter for "inaccuracies" and "errors" for the construction of the bookcases (eg. distortion, rotation, shelve bending).
Building in Houdini is a really enjoyable & satisfying experience (especially when things work the way you had planned).