Look up "Application examples for LOGO!", download, read the source.
also random googling gets you "I have found a useful tool for studying communication protocols of LOGO under setup directory Program Files\Siemens\LOGOComfort_V5\lib\classes.jar..." doesn't look like HTTP at first glance, not even clear if it is based on tcp and not, say, udp, yet it does appear to be a good start, try to recreate that chap's dev environment and I think you're solid.
also below, assuming you have same generation controller:
http://wiki.ibhsoftec.com/en/OPCServer:Variables_from_LOGO!_RCE
and here's a library, supposedly supports C#:
http://www.adontec.com/index.htm?GO=/s7-library.htm