I understand the reason behind not going to a mechanic for the sake of saving money, but you've definitely wasted your time and more than a few bucks by replacing parts without diagnosing the problem first, and then on top of that, potentially damaged the engine further in the process.
As boofoo pointed out, it's probably a blown head gasket. When the car over-heated, the coolant went past the head gasket and entered the combustion chambers. Now, fuel, air and spark cannot properly ignite to create an efficient explosion, thus, the rough idling/no start condition. Did you notice any white smoke coming from the exhaust? When you removed the spark plugs to replace them, what did they look like?
Do not attempt run the engine at this point anymore, instead, open the cap on the radiator and check to see if there is oil present. Then, remove the oil dipstick and check for signs of coolant or water-like drops (milky oil). Next, remove the spark plugs and check them for signs of oil/coolant mix. While the spark plugs are out, take a flash light and look inside the chamber to see if there's any obvious indication of coolant.
If all of the above steps do not show signs of contamination, you'll want to perform a compression test. Based on your opening post, I suspect you will not be familiar with how to properly perform one (no disrespect), so consider taking the car to a reputable mechanic, where it can be properly diagnosed and repaired accordingly. The head will need to be removed to asses the damage, hopefully the block is still in decent shape.
Good luck, let us know how it goes.
