Hi Himali,
Why would like the system partition to be a ramdisk? As its name suggest, the ramdisk will be located in RAM, the system partition takes about 300MB which is the amount you'll lose. Plus be aware of the ramdisk size limitation: https://www.kernel.org/doc/Documentation/blockdev/ramdisk.txt
If you really want to do so, I'd say to have one ramdisk which would be rootfs + system partition. Then you'd need to modify fstab not to mount /system as already present. But once again I'm very curious about the reason that makes you think this is a good idea.
Regards,
Gary