Just gather up all your friends and shovels, find a solid spot and start shoveling the snow into 2 mounds (kicker + landing). Once you have what you feel like is enough snow, go get some more because you need to pack it down hardcore. When you actually get it stable enough to stand on/ski off of, then you can shape it and get it looking all cool.
If you have an ATV I suggest you use it to tow people in, you can hit much larger gaps that way. They also come in handy for bringing snow to your spot (if you have a trailer).
I usually end up spending about 2-3 hours making a pretty huge jump with a 3-man crew, but it varies.