I figure we all have our own ways of building our props. I had surgery on my knee and am laid up a bit and finally have time to do something I've wanted to do for a while and give back to the site from which I've gotten some good ideas. Here is my way of making props. Probably not the best way, but it works for me.
I generally get costumes and other things from Kmart about 1-2 weeks after Halloween for 75-90% off. When I build the props I make frames from wood, copper, mannequin torsos, styrofoam heads and pool noodles. The nice thing about using copper is that it makes posing the props very easy and you can change them daily or yearly. Here is a zombie I made over spring break. each one takes about 1-2 hours to make.
I got this costume from Kmart for under $5. You can also get suits, shoes, belts etc.... from goodwill for very cheap prices.
I cut the wood into different pieces to make the basic frame. The finished props are sturdy and very lite. I make the bottom of the zombies wearing pants different than the props that consist of dresses and robes. I use rebar driven into the feet of the props and the ground to set up the props in upright and action positions.
I cut the wood so that I have feet, legs (cut at the knees so that they can be posed, waste and spine.
Once the wood is cut, I start framing things out. I attach joints using flexible copper that I got from home depot. I originally used 1/2 copper but wound up having to go back and doubling up the joints. I've found that 3/4 in flexible copper is both sturdy and flexible for the joints. You drill holes and then tap the copper into the holes. Sometimes it's loose, sometimes its not. If the copper does not stay in the holes very well, just use and adhesive to add the extra friction to keep everything in place.
Once you have the legs framed out, add the mannequin torso. They work well for zombies since they are thing, but also fill out the costume. I attach the torso using decking screws and a couple of different methods.
Here's a picture showing how I attached the spine for this zombie. I went straight through the torso into the wood using copper as the connector.
Here's a different zombie where I wedged the bottom of the torso between two pieces of wood.
Once you have the bottom of the spine attached, you want to set it up so that you can attach the head. I use a basic styrofoam head with a wooden dowel rod placed into it. I drill a hole in the spine, put a piece of copper in it so that it is flexible, and the other end of the copper goes through the upper part of the torso into the dowel rod, which goes into the head.
Normally I would cut the neck of the styrofoam head off, but was experimenting trying to go for a more freakish look.
Once I get the main part of the body done, I run copper through the torso and spine for the arms. If you are just posing it, 1/2 inch copper is enough, if you plan on having the prop hold something, or are making a prop that will be on all fours, 3/4 copper is better.
You need to crimp the copper using channel locks to make the arms solid and keep them from flopping all over.
Once you crimp the copper, duct tape or gorilla tape the copper into place.
Once my frame is set, I like to flesh things out using pool noodles that I get from the dollar store. Probably not needed for the legs, but definitely makes the arms look a lot better.
I forgot to take pictures of the pool noodles arms with this zombie, so here is another one to give you an idea of what I did.
For the rest of the arms and hands, I like using those groundbreaking lawn stakes you can buy for Halloween. Amazon has them for like 7-$8's shipped. Some are skeletal, some are in the shape of hands. I put the end of the copper down into the hands and Gorilla tape the copper and arms together. It is actually really solid.
In the end everything comes together like this. The zombie is standing without any support here. When I set it up on the lawn I will drill 1/2 inch holes through the shoes, into the feet and legs. I will then hammer rebar into the holes and put the other end of the rebar into the lawn. This has been extremely sturdy staying in position in heavy winds.
Here are some of the props I have made using variations of the above method.