It would be quite difficult to provide an exact estimate because when you are assembling the parts there can be wide variations in the prices of the parts with different vendors and shops.
However, with your requirements you should be able to assemble a desktop within Rs.30,000 price range.
Here are the parts you should go for:
Intel i3 dual core Gen 4 motherboard from ASUS - Price Rs.7,000 with 3 years manufacturing warranty. Do check it has support for USB 3.0 and has memory slots for graphics card.
NVIDIA 2GB DDR3 graphics card - Price Rs.3,000
WD Internal hard drive of 1 TB - Price Rs.4,000. You can go for Seagate too but totally avoid Toshiba hard drive.
Cooling Master cabinet which should come at around Rs.6,000 max.
Corsair Smps which should come for around Rs.4,000.
Keyboard and mouse are more of a personal choice. You should check these online, I think if you are want to do gaming then a gaming mouse from Logitech will be a good choice and will cost you anything from Rs.1,000 to Rs.5,000 but I would suggest you to go for G300 mouse from Logitech which will cost you Rs.1,500.
Keyboard again you can get a good one for around Rs.1,000 to Rs.2,000.
DVD writer usually go bad within 2-3 years so I would suggest go for a mid range one which won't bite you much when you replace them after a few years. You might not even need DVD drives much if start using virtual disk mounting softwares with which you can install your games and any software set up in a .iso.
Monitor you have already selected the right size. Go for a Samsung monitor, they are the best in visual quality.