I need to find out what size of boards to use and how do I put them together.
Well it all depends on what size you ate making and how big your window is. Look on you tube or pintress for tutorials . Ask how to make a cabinet with an old window? Then adjust to your size.
Here's a tutorial I found, but the size of the sides will depend on the size of the window.
Making a cabinet that is stable, squared, and level, is not a simple task.
If you do not have any previous experience in cabinet construction and all the specific tools required, I would suggest purchasing a ready-made cabinet, then switch out the door with your window.
Depending on the width of the wood on the side of the glass on the window, you may also be able to use the same hinges.
Decide the depth of your cabinet . Then build a frame the size of the window , add a back to it . Then add any shelves , you can drill holes to allow you to put in shelf holder hardware or put in a piece of 1/4 or 1/2 found tri. To support the shelf . At Lowe's or home depot , you can buy different shape & height table legs , attach the legs . Now , attach 2 hinges to the door and cabinet and finally , attach either a magnetic closure of latch . Paint or stain !
Do you have a picture of your old window?