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