If you want to purchase things based on sales, I recommend the following:
1. Buy the case (or whenever, you don't need other components to see if the case is damaged)
2. Buy the CPU, MB, Ram in a group (reusing the PSU will allow you test them at once)
3. Buy the GPU.
And then other things can wait, you might need to juggle hard drives and operating systems, but Its not that much of a headache.
I don't know when components typically go on sale, but just watch them and then buy when the prices fit your budget. That is what I did (but when prices were much higher )