I've used the disposable aluminum roasting pans successfully. I can reshape them to accomodate an extra pot without wasting any space and they come in so many different sized that I can use up ALL the space on the shelves. When they get too beat up I poke holes in the bottoms and use them for the actual planting pot, especially for ground cover type seeds that just get picked up in clumps and set in the beds when they're mature enough. After the Christmas holiday last year I bought up all the serving trays from the dollar store at half price and used them to set under larger pots when they went into my kitchen or sun room.
