I wanted to start building butthen someone warned me to wait for DDR4 and the new intels. What is your opinion ? Will it be a huge difference for gamers/editors ?
The first line of DDR4 memory coming out is not expected to be much faster than current DDR3 with high clock speeds. In time as production improves DDR4 clock speeds will improve but it will take some time. Even with those future faster DDR4 modules gaming is not likely to see much of a benefit since games aren't starved for RAM bandwidth today, with the exception of integrated graphics.
Only maybe wait if you feel you're building a workstation and are prepared to pay about $999 for the Haswell-E eight core i7-5960X. While it's not going to run games any faster than say an i7-4790K, video editing would be noticeably faster.
Go ahead and build. Hopefully by the time your ready for another machine you'll be building with DDR4