Good stuff everybody! About three years ago I got back into paintball for the first time in about 10 years by playing some recball/woodsball on a friends small field around Thanksgiving. That's all it took, and since then we've been constructing our own field on roughly 5 acres of wooded family property.
We wanted this to be a pretty nice, functional field for various game-play styles, but we also wanted it not to become strictly a "speed-ball" course out in the woods. We were also on a pretty tight budget (gotta keep the wife happy), so first thing we did was contact a local plant in town who was more than happy to off-load some of their old pallets to us. Pallets are great. Double stack them, break them down for the boards to cover the slats, use branches and limbs to fill in the slats, nail/screw them into trees to make them more secure, the options are almost endless. We incorporated the pallets into other forts/bunkers we made using fallen trees/limbs, cleared paths/trails and dug a bunker out and made a pill-box type of structure as well. We built a tower/look-out post that becomes a hot zone pretty quickly and functions nicely as a deer stand during hunting season
We also used some garage door panels that my dad had damaged and had to replace, and they are fantastic bunker builders.
All in all, it's a matter of what you want to get out of it I believe and the style of play you want. It's going to take work, but that's part of the fun seeing it all come together.