I wouldn't put styrofoam in there, but sawdust is....okay. I wouldn't advise it either though.
The best bedding for the floor is either kid's sandbox quality sand (which basically means that it is actually clean when you buy it) small wood chips, wood shavings, straw, hay, or pine straw (long pine needles).
The reason why, is because sawdust is so easily stirred up and the dust can cause open up doors for respiratory problems for both you and the birds when you have to breathe it.
Shavings are good because there is less dust produced, and it keeps the droppings on the floor dry. Straw and hay do the same, with less dust, but bugs can easily live in the hollow straw, so you should put down some Diatomaceous Earth or Sevins dust first, then put down the straw/hay on top. Same thing for the pine needles, although it isn't as bug friendly, it will still make a good place for them to live under the needles. Another thing to keep in mind, is straw and hay can grow mold and bacteria quite easily when left wet. So you don't want them to take baths in there where they could spill water on the bedding. Pine needles aren't as moldy though.
Wood chips of course, probably produces the least dust of the wood products, and it (as will any bedding) will help keep the floor dry, which is a must in disease control. Clean sand acts like a literbox, so if you can find it, it's wonderful. Plus the birds can safely pick at it as grit.
Whatever you use, just remember that it's important to rake the bedding around every day. Not only does it aid in keeping the droppings from staying wet, but it also makes good use of ALL the bedding, in that new, clean material will be moved to the top. Then, once every week or so (depending on how many birds and what you use), you can change out the bedding for fresh material.
Right now I have a thick bed of straw in the loft, and the birds LOVE it. They really like laying on the straw, especially the younger birds. Plus the older birds have plenty of straw to use for their nests!