If you want us to make a custom
plugin for you, you'll have to at
offer us something in return. If you want to sell the plugin we
make in any form, you're most likely going to have to pay a license fee.
We're a very busy bunch who mostly make plugins for fun. So, if your
idea isn't at least fun or breathtaking or ... and you don't want to pay
for it, don't bother. And please, no requests like "make a plugin like
XYZ's ABC plugin but better", we don't want to fall asleep coding.
Here's another hint: 85% of "custom plugin requests" can be answered by
pointing to a more advanced host application. For extra, ultra-flexibility
you should check out apps like Plogue Bidule
(Mac OS X and
(Mac OS X and Windows), and then
there is even more hardcore stuff like Csound
(many operating systems),
(many operating systems), etc.
In some of these hosts parameters can be modulated from external sources,
be it audio, data, sequencers... i.e. you can use a plugin, and enhance
it's functionality with LFOs, envelope followers, etc.