Should I sell my ps4 to build a $500 computer?

I wouldn't. A PC for $500 is going to be less powerful than your PS4 is meaning you will not be to play new games on it. If you really feel you want to play with your friends that badly I guess go ahead but I couldn't recommend it.

No man… Never do it! The ps4's amazing games will start to be released in 2016!

As already said, a 500 dollar computer won't play newer games. I have an 800 dollar laptop that barely runs Diablo 3. An actual tower would be more powerful but not for 500. Plus if you want to get into PC gaming you need to also take into account the fact that every couple years you'll have to upgrade the computer and eventually it will hit its maximum specs and you will end up having to buy a new computer. I don't know your situation but I'd recommend hanging onto the PS4 and start saving up for a computer. That way you'll have access to both.