I'm giving a workshop on the design and construction of Arduino shields on March 24th at Metrix Create:Space in Seattle, from 7pm to 9pm. Like all Metrix workshops, the cost is $50 and you can sign up online or in person. Here's workshop description from Metrix's workshop page:
Arduino Shields
The engineer behind Logos Electromechanical teaches about Arduino Shields: One of the neat features of the Arduino platform is the ability to mount peripheral electronics, such as those taught in the Arduino I/O workshops, onto permanent daughterboards called shields. This workshop will survey the wide range of shields on the market and lead you through designing and building your own motor control shield with built-in speed control.
Participants will need a laptop, an Arduino, and a USB cable. A protoshield and other required components will be provided.