Having gotten some help around here on how to power my 2m mobile
indoors cheaply, I need to figure out a way to get an antenna. There
are probably a million holes in this plan, please point them
all out to me!

I intend to get a piece of square sheet metal (ground plane?) about
half a meter each way, and build a bracket to hold it outside my window
horizontally. In the center of the sheet metal I'll install an NMO
mount for my mobile antenna. I'm actually planning to ground the sheet
metal using the electrical ground in the wall socket (surely
something's wrong with THAT!) I look forward to better alternatives!