Hello Sudha;
Interesting project.
To gather the data from the 60 PLCs in the project, you will need some software on the PC that can handle the communication protocols you select, log the data in some kind of database and then make it available to the ERP software package.
So I think your idea of using WinCC as a data collector, then using it as an OPC server to make the data available to the ERP has some chances to work (if the ERP has an OPC client integrated).
First step, would be to select the communication channel between the S7-200s and WinCC. Here are some documents on Profibus and Ethernet connectivity for the s7-200 and WinCC:

http://support.automation.siemens.com/WW/view/en/14587200

S7-200 Profibus with WinCC

http://support.automation.siemens.com/WW/view/en/14509682

http://support.automation.siemens.com/WW/view/en/21915525

You would have of course to start by implementing adequate topologies for the communication network you select. Profibus is a line bus, allowing up to 123 slaves to connect on a daisy-chain structure. Since your project holds more than 31 slaves, at least one repeater has to be introduced in the network. Bus length and speed of communication are interrelated: 12 MB for 100 m segments, 500 kB for 400 m segements, etc... Each slave can be conigured to transfer 244 bytes OUT/244 bytes IN, but if every one transfers the maximum valueperformance will be affected.

For Ethernet, you would generally use star topologies, with hubs/switches to connect the different segments. Segments cannot be more than 100 m,whatever the bus speed implemented with cables and switches. you must make sure that the amount of data does not cause too many collisions, or comms will break down.
Once the data is read into WinCC, as WinCC is an OPC Server (as well as an OPC client) all it's tags are available to an OPC client. The client (your ERP sopftware package) just needs to connect to the WinCC OPCServer on the WinCC machine and it will be able to browse all the tags in the project.

Hope this helps,
Daniel Chartier