i want to build a gaming cpu @ 400 usd / 18000 rs

Well with that budget that is really hard to do with. But if you have an extra, hdd, cooler, display, speaker, and those kinds of unnecessary things that you can maybe get from your old computer, then you can get a much better specs.

For $400, you're probably going to need an AMD Processor. They're great for multitasking, high quality multimedia, and gaming. Depending on how much you want to spend on the processor alone, you have several choices, I'll list some of the ones I suggest here: AMD Phenom II X2 - $85-$130 AMD Phenom II X2 Black edition - $100-$150 AMD Phenom II X4 - $120-$140 AMD Phenom II X4 Black edition - $130-$180 To help with cooling and to reduce the cost of the case, try to get a case with as much airflow as possible. While gaming your CPU will get extremely hot, as it will most likely be at %50-%90 CPU if you're doing serious gaming. Generally, CoolerMaster cases are designed the most sensibly as far as cooling goes. Check them out and find one that fits your budget. Worst case scenario you could run your computer in an old PC Case with the sides removed. You probably wont need an HDD any bigger than about 250GB, which will run you about $30-$60. When choosing a motherboard, just make sure it supports the AM2+ Chipset if you chose one of the processors I listed. You may also want to take the maximum installable memory into mind. I'm not sure about graphics cards. Good Luck! Luke