I think you're better off having a sloped roof, and a balcony/deck coming off the side, ie make the platform bigger with a open area on the side of it, I think a flat roof is asking for water damange to occur much more quickly.

Quite windows would be my first choice....whatever you choose. Another option would be to buy plexiglass, or some sort of clear plastic sheeting from a hardware store and create the slide windows yourself....could be quite a big cheaper and possibly better....quieter and easier to open/slide.

Also plan to make the enclosed area big enough to draw a bow....read a story years ago in IL Game n Fish a guy built a blinde, for his father/rifle, ended up bowhunting out of it and it was too small to draw on a deer.....stuff like that shouldn't happen, design it for all options...because eventually all of those options will happen.