"Slanted/Attic" Type Ceiling? Good? Bad?

I am trying to decide which room in my house to use as the control/mixing room. There is an upstairs room that has slanted ceilings. What I mean by this is that the two parallel walls facing in one direction are just straight walls up. These walls are about 12 feet wide along the floor. The perpendicular walls go up about four feet and then slant inward at a 45 degree angle with about a four foot flat section at the top/center at 8 feet tall. These walls are longer at about 20 feet along the floor. Would this be a good, bad, or indifferent situation for a control room? I could either have the desk along the flat walls and have the slants to the left and right of my head. Or I could put the desk along one of the longer walls in the center with the slants to the front and back of my head. Which would give the best results for stereo imaging, modes, etc.? I don't really know much about room acoustics so any help would be greatly appreciated. The section view of the room facing the shorter wall would look similar to this crude shape in red: ...____ ./.......\ |..........|

I'm sure that room will be fine. Set up with the speakers firing the longer way down the room. More here: How to set up a room --Ethan

Thank you for your response. I have at this point decided that I will not use this room. I have decided to use the basement instead which, if you like, you can see in my post here: http://www.johnlsayers.com/phpBB2/viewtopic.php?f=1&t=11700