This may be a dumb question but I'm new at this.how long and wide should they be?should they be covered in shavings?ive also heard of using some sort of plastic tray,which would be better?
there have been whole threads on this; if no one answers your question, you might try doing a search in this section of the forum, but use this to search:
It does depend on your approach. Me, I like to do a few minutes of cleaning every day, rather than a hour or more of major cleaning once or twice a year (that's why I don't do the deep litter method).
I like to clean out the droppings trays every morning. I use plastic boot trays because they're light and easy to lift up. I simply take them out, dump the contents into the composter, hose them down, and replace. All but the cecal poops slide right off the plastic (and the cecal poops hose off). Adding shavings to the tray simply wouldn't be necessary for my method, and would be a hassle to replace every morning anyway. However, if you weren't going to dump the trays daily, shavings (or sand) would help to keep the smell down by drying out the droppings.
As far as length and width, what you're aiming for is something the length of your roost, and wide enough to catch poo whichever way the chicken happens to be roosting (bum toward the front and bum toward the rear). The trays I have are around 20" wide (I think) which catches all the droppings from my bantams.