How I make my armatures

I have found that I can get metal coat hangers cheaper than I can get thick crafting wire,  so I use this for anything that needs to be strong. I use florists wire for more delicate things like wings.

I use metal epoxy putty for all the joins.  It is clean to work with  (if you use gloves) and sets very quickly. Once set it is as strong as if you welded it.

I then use scrunched up tinfoil to fill any large spaces  (like the body of a horse) and use masking tape to hold it in place.

Once I have finished,  I cover it all in masking tape.  This is because my clay will stick to masking tape,  where it will slide on the smooth metal. 

Also, trying to cover tinfoil in clay without the tape is a disaster! You wind up with loads of it poking through the clay, where it's not gripping.  That was a really annoying day,  learning this the hard way.

I would also like to mention that you need to check that you are making it in a pose that will hold well and look natural.  I  look online at pictures of the thing I am trying to make. 

As a rule,  if your armature falls over when you put it down,  then so will your model.  It is possible to change this by the weight of the clay,  but not easily.  It's far easier to get it right at this stage.