I would like help with designing a patch that

• lets me select a midi pitch and then
• using additive synthesis helps me generate repeating cycles of complex sine waves

Anyone who may have similar patches of such a nature please let me see them so I have a good idea of how to go about this. Cheers!

could you be more specific? for instance when you say complex do you mean that you need the real and imaginary part of the sinusoids?
as far as I know no one's programmed an external for an arbitrary amount of partials, check out http://msp.ucsd.edu/techniques/v0.11/book-html/node71.html and the example in the help he refers to. I think you need to decide in advance how many partials to have.
Basically: multiply the fundamental by the harmonic, then put that into [osc~], then get that sinusoid to the correct volume with [*~ ]