how about the excellent one from the wiki ? (it explains step by step how to create a dll)

http://www.opserver.de/wiki/index.php/Writing_a_basic_DLL

get the C# wrapper:
for A7.85.4 and A8.30.4, Version 2.3.9
at http://acknexwrapper2.matthias-auer.net/ or visit the thread