(This is going to be short, too short for a tutorial, so I'll just post it here.)

Okay, over the past few weeks I've had people ask me/heard about people having problems with their custom player models. That problem: The sink into the ground, down to somewhere around their thigh.

Well, this has to do with your model's offsets. Most likely, they're set to "0 0 0" so JK puts the model's hierarchy's center on the ground, instead of the feet.
Pretty quick, simple fix: you want to replace those numbers with higher ones, so the model gets raised up to where is feet appear on the ground. The numbers I use are as follows: -0.000050 0.000000 0.120000
Now you want to use these numbers for the skin's "offsets," so what you do is you open your model in wordpad (or some equivalent) and scroll down, just past the materials list, under SECTION: GEOMETRYDEF
There should be an INSERT OFFSET # # # there (if not...you have bigger problems...) Just replace the numbers there with the numbers I've provided and you should be set.
If you have any problems, I'd prefer you post them in reply to this topic rather than emailing me, thanks.

Happy modeling!

-TIE

Or it could've been the floor was not flagged as a floor or the walkplayers weren't placed above the floors.