I'm planning to build a gaming PC for 700 $. I'm also planning to get 40 inc screen couple months later, so I'm probably going to use 2560x1600 res. for latest games.(Such as Blade&Soul, Tera online etc.)
I have 500W power supply (No idea about the brand)
Regular size case (No idea about the brand)
I'm not going to overlock it, so I prefer intel based builds.
Check out these builds for $650 and $850. You could almost do the $850 build for $700 because you already have the case and PSU but the problem is that 500w might not be enough for this build. You could obviously financially do the $650 build since it is build around at 500w PSU.
P.S. You might also want to look at this PSU calculator since you are limited to 500w. Come up with some of the parts from the builds above that you might want and then throw them into the calculator to see how close you get to 500w. You should be able to keep it pretty low without dual GPU's and no overclocking.