HD does sell 16" wide pine board, about 1" thick that would be fine for a shelf if you want a raw wood. They also sell 15 1/4" mdf pre painted in white/black/tan. The problem with a 16" deep shelf is supporting it. You could buy some heavy duty brackets but they would probably be $10-$15 each for such a big size
You can find brackets like this that have an integrated loop in the end, so you can mount a bar right below the shelfs edge to hang the drapery you were talking about.
Your definitely going to want to screw the brackets into the studs behind the drywall with a 2.5-3" wood screw. Be sure to have all of the brackets square and level so grandma is impressed
You can find brackets like this that have an integrated loop in the end, so you can mount a bar right below the shelfs edge to hang the drapery you were talking about.

Your definitely going to want to screw the brackets into the studs behind the drywall with a 2.5-3" wood screw. Be sure to have all of the brackets square and level so grandma is impressed