I suggest looking through some of the major hunting supply catalogs like Cabela's for some ideas. I just recently saw some base kits, of course I can't find them now, that provide metal base brackets, with the correct angles and adjustability for leveling, to make construction easier. You only need to supply the wood and fasteners.
You did not mention whether you are placing these stands in open fields or in the woods. With woods, the use of trees make the construction much easier. If you are putting them in the woods, ladder type stands are safe and easy to construct, with the tree providing the third leg.
If you are making them out of pipe or angle iron I can't help you much, other then to say look at all the available ones in the catalogs. Good hunting.
