The most valuable tips I can give someone who really needs or wants to trap hogs is this. Trapping requires time, money, dedication and equipment to be really be successful ( 4 wheelers, chain saws, weed eaters,custom trailers for the 4 wheeler, feed trough, water trough, and the list goes on). I have my own welding shop and I am an accomplished welder.
Being able to build these fancy gadgets and not pay to have them designed and built is an advantage. So,, for those interested I will do my best to explain these gadgets and ways I have found to trap more hogs.
# A trapper, in most any situation, who sets a trap will generally scare the hogs out of the area for a period of time. How long this time may be is dependent on the population and education of the hogs in that area.
I have, on rare occasions, caught hogs the first night but in most situations a trapper should expect the hogs to stay out of the area for a while. In some cases, depending on the population, they may not return for months or not at all. That is why I encourage extensive scouting to make sure that the sign in the area indicate an existence for at least one year. (if the trails are worn deep and used every night then I would consider it worth trying) (if there is hog rooting but no indication of a regularly used trail I would be reluctant to go to the trouble of erecting a large or permanent trap unless crop damage was occurring) You best bet would be to try and simply shoot'em or scare'm off to begin with. If you need some assistance I CAN HELP. Feel free to e-mail me for assistance
# The first thing I would do is look for well worn trails and other sign discussed in the SIGN AND HABBITS PUBLICATION. When all of the right sign is present I would then be convinced a trap will work.

The signs to look for would be a heavy trail that is used on a regular basis. There are established wallows in the area and rubs which are used regularly. Woods that are large enough to hold multiple sonders that frequent the area. Look for a trail coming from dense woods and under growth leading out to feeding areas such as pastures or crop fields (the trail can lead anywhere). It is very important that the trail exist.
To know how many cattle panels you might need here are some different size traps and the panels it takes to make them. Pay attention cause I'm trying to be brief. I also describe how to DIVIDE and USE each panel in this section
Traps made of cattle panels will be 4' high and require at top.
Sheep panels 5' high are OK with out a top. The sheep panels I refer to are 20' long and 5' high with squares that are 4"x4" (they may be called something different elsewhere). Sheep panels are preferred but are also more expensive. They can hold the smaller pigs and the large ones too. They are tall enough that MOST hogs can't jump out and the injury to the hogs are not as common. These panels are also stronger.
REGULAR CATTLE PANELS  are generally half the price of sheep panels. They have larger holes and allow smaller pigs to escape, require a top, injure more hogs in the mouth area and and the panels are damaged easier.
When using cattle panels which is the most common I would use at least two panels. This would make a trap 8'x12' (96 sq ft). One panel would make a trap only 5'x5' (25sq ft).
WITH 2 PANELS you can make a trap 4'x8' USING ONE PANEL for the two sides, by cutting it in half. Then make the TOP and TWO ENDS by first CUTTING A PANEL IN HALF and then CUTTING ONE OF THOSE HALVES INTO AGAIN.
With 5 panels you can make a trap 8'x16'. For the TWO 8' ENDS (one will be a door) CUT A PANEL IN HALF. Then USE THE REMAINING FOUR PANELS for the TWO SIDES AND THE TOP.
Creative thinking can result in traps larger or smaller. The larger a trap is the less likely a hog will try to jump out and the more likely you are to have multiple catches. I have traps made of 4' high panels that are approximately 100'x100' and trapped very large hogs and many at a time. None have jumped out because there is room to run.
TEE POST ("T"POST) as well as a driver to knock them in the ground.  4 "T"post will need to be placed along each full length panel or a T post every 4 or 5 feet. Strong Wire will be needed to tie it all together on-site. Maybe a few other things but that is the basics.

HOW TO BUILD WILD HOG TRAPSIf further information is needed.

HOW TO BUILD A WILD HOG TRAP (FREE VERSION) This FREE release is an updated version of the early Power Point Presentation! YOU CAN NOW View the presentation on-line!

The doors are really simple but explaining them may be difficult for me.
Because of the e-mail requests I will jump right into the trip mechanism of a Guillotine Trap Door.
working latch for trap door.
THE TRIP MECHANISM is simple but requires some tools to build. It is hinged onto the inside frame of the trap. A light trip wire (light picture wire is cheap and works the best) is attached to it and is run through the trap where the hogs will hit it. As you can see when the wire is hit it will pull the latch and release the door.
The two hinge points are important for the latch to work at its best. If the top hinge shown on the diagram is not used on the latch  it will impede the operation of the latch. A horizontal latch may also be used (below).

It requires only one hinge point (works better with 2) and is mounted on top of the trap frame. A horizontal mechanism is quicker and simpler to build if a builder does not have the tools to work with.
The door is simply placed in a set of slides that allow it to fall. The slides can be angle iron or channel iron as shown in the diagram below. Deep Channel Iron is the best
 #tip When trip wires are set, make them high enough that coons are smaller hogs won't hit the wire. I like two set mine about 2' high. (if a smaller hog trips the door the larger hogs outside the trap may get educated and never come back) The baby hogs are not educated and less cautious so they will go in first most of the time. This will increase the odds of multiple catches.
As I mentioned earlier it is a must, that a catch be placed above the closed door. Hogs can raise these doors no matter how heavy they are allowing others to escape. In the diagram below is shown a simple catch made out of  1\2" wide x 1/8" thick x 18" long flat steel. This will be springy enough for it to spring through an opening in the slides over the door frame keeping it closed. This is shown in in the diagram of an complete trap door below.

Hopefully I have done well enough for a person to understand the basics of building, placing and setting a trap.