Hello Syed;
A SCADA system is a Supervisory Control and Data Acquisition package that interfaces with a plant/process control system, generally a PLC. It allows operators to send commands to the control system, recieve information, status and alarms from the process, while building databases to archive the required information from the process.
Basically, what you need is a PC, SCADA software and communication drivers/interfaces to connect to the control system.
Examples of SCADA software available on the market:
-RS-View, by Rockwell
-WinCC, by Siemens
-Citect, by CI Technologies
-Wonderware, by Intellution
-Fix, by GE Fanuc
-Cx Supervisor, by Omron
Hope this helps,
Daniel Chartier