Have you ever touched an airsoft gun before?
How would you know how to make it 'reliable and accurate' if you don't understand the system to begin with.
If anything, learn through a cheap AK clone like an Aftermath Kraken. But beyond that we can't really help you much. Get verified here and purchase a realsword as mentioned before. Its either you waste time and money on a scratchbuild whilst blindfolded. Or you spend good money on a quality product without much hassle..