Custom Base Type in C

I have been trying to created a custom base type in C to use as a state transition variable for some aggregate functions. By following the documentation I haven't been able to do much but crash postgres :) I can compile and run the complex example from the tutorial just fine so I guess that means I am compiling correctly.

My custom type needs to have one biginteger and one text value... pretty straight forward. I guess my first question is if there are any examples out there that do something similar. I have looked extensively through the contrib directory and can't find anything very helpful. If not, could someone help me understand what my c struct would look like and what values I need for INTERNALLENGTH, ALIGNMENT, STORAGE, etc in the CREATE TYPE command?

Thanks a ton,

Toby