Some home centers sell larger sheets of Plexiglass or Lexan but those are generally clear. You might want to try a glass shop if you need something opaque or translucent rather than clear.

Thanks but I should have mentioned that it needs to be flexible to fit over the shower head. I need something that can take some bending.

You could use polycarbonate twinwall panel. It might be opaque enough, and it will not sag. Our building supply houses carry it.

Here is a link that might be useful: Polycarbonate Twinwall Panels

Thanks Blindstar, that would work. To tell the truth, I'm looking for something a little cheaper since this is a temp fix for a few years until we redo our master bathroom and enclose the shower. But I'll check it out since it will bend enough.

They have those type of clearish panels for drop ceilings for lighting, maybe that would work.

Our local True Value hardware store carries 4x8 sheets of plexiglas and will cut any size you want. Different thicknesses too. Menards also carries up to 4x4 sheets of some kind of clear plastic. Not plexiglas, more expensive.

We do have True Value HWs around here. I shall call around. Thanks for the idea. I was thinking that perhaps lighting stores might carry larger sizes of flurescent fixture sheets.

Think glass replacement stores. You will have better selections.

Fluorescent fixture diffusers come in roughly 2' x 4' sizes because that's the size of the troffer. It's also acrylic, which can be difficult to cut and it does break, sometimes rather easily. Lexan, which is a brand name polycarbonate, does not break anywhere nearly as easily as acrylic.

Can I ask exactly why you are trying to enclose the top of your shower? Maybe if you tell us what you are trying to accomplish someone would have another suggestion.

My master bath has a ridiculously high ceiling: up to 20', so during the winter all the warm air rises rendering the shower rather uncomfortable. By enclosing the top of the shower stall, I hope to keep a warm area for showering by preventing the warm humid air from rising. Eventually we will redo the bath and put in an enclosed shower.

The shower head rises slightly above the top of the stall so a flat piece of plexiglass or other stiff plastic sheets won't work. The sheet needs to bend 6" along the short side of a 3 X 4' sheet in order to make a neat solution. I could always rig up something with 5 mil plastic sheeting but that would look sloppy.

I'm running out of ideas. The hardware stores sell plexiglass which is too stiff and much too expensive for this application, otherwise I could take two 4 X 2' pieces and contruct a peaked roof without needing to bend anything. Actually, all the material needs to be is waterproof. Any ideas?