I am planning on replacing a rotten wood window in our concrete foundation.

I don't need the window to open so I was wondering if I could use 4 pieces
of treated 1X8 to form a box that just slides into the opening & fasten it
with a couple of concrete screws. I would install a glass stop on all 4
sides with 1/4 round then have a sealed triple pane glass unit made up to
fit & seal it in place with silicone.

Two questions:

Do I have to slope the lower sill to allow water to run off?

and

Is 1X8 stock good enough (or should I be using 2X8)?

Thanks