1. No..there are currently no octagon or cone shaped roofs. You can use the hipped roof and curve it to get an interesting shape..you cal also put a couple of roof sections together. Builders in the Lots section of the forum have been coming up with all sorts of creative ways to handle this...I would suggest you pop in there :) http://i226.photobucket.com/albums/dd250/ruthless_kk/curvedroof.png
2. to activate auto windows, click on the room symbol next to the window that says "by room". This places windows at regular intervals by room...not the whole house. Everything in the new system is room based. http://i226.photobucket.com/albums/dd250/ruthless_kk/autowindow.png
3. the section without roof tiles is not being considered part of a room. Since everything is room based, in order to fill that in it needs to be part of a room. I would go and place an octagon room shape there and it will fill in. http://i226.photobucket.com/albums/dd250/ruthless_kk/fixroof.png You should be able to place roofing over it by simply hitting page up or page down until you are on the right level. Once the grid is visible, you can place a roof.
4. Because of the room based build system, you can only delete all of the floor tiles of a "room" or none. No in between. So the area that you want to be an open must be its own room and then you can delete the space. http://i226.photobucket.com/albums/dd250/ruthless_kk/rooms.png So basically the landing or loft must be seen by the game as a complete room and the empty space itself is another complete room...if that makes sense. http://i226.photobucket.com/albums/dd250/ruthless_kk/loft.png