Need a little advice replacing basement window
I have a walkout basement in which I am finishing a room on the walkout side. Currently the room has old metal windows set into the cement foundation wall. I plan on removing the windows, frame a 2X8 wood box and gluing/ nailing the box into the hole and then install the window.
My question is this, when I remove the window the bottom cement is slopped downward enough so if I put a bottom plate in, there will be a 1.5" to 2" gap at the outside edge between the wood and cement wall. What is the easiest way to deal with this? Cut the bottom flat? Build the bottom up so it is flat? Install the framing then fill in the gap?