Well.. if you are planning to buy the parts as you get the money is a bad idea. My advice would be to collectively save the money and then get the parts when you have saved the money.
The recommendation above is because :
--> If you buy the parts now, then they might get cheaper in the future and then you would not be happy.
--> You can get much better performing parts for the same budget in the future than what you can get now. The prices drops and more powerful things become cheaper.
--> If you find something very good, then you would spend more than what you should on that particular component and hence you would end up spending way more than what you should.
--> Things may go opposite to what you may have planned, like you bought a Motherboard for an AMD CPU, but they you might want to go for the Intel and then you would have to stick with the AMD since you already bought the board. Similar things can be attributed with Case Size (ATX, Mini ITX, etc) and other components.
Hence my advice would be to save the money alltogether and then spend the money collectively, that way you would be able to get much better parts for the same budget.
I hope this helps. You and everyone should follow this method only.