[sch]

Thanks for your help.
A new retreat for the whole family is in the making and I've been awarded with the chance of having my listening room. The architect just sent me his first drawing. I told him to try and design with a non-parallel wall.
Dims are in meters ( 4.20 meters = 13.8 ft ; 4.00 meters= 13.2 ft; height will be 9.20 ft).
I think that length must be higher from 13.8 to 16 ft..
But my main question is if the angled wall will help with the sound or not?
Of course, I am planning to seat away from the back wall.
I haven't decided on the speakers but I think I'd go with small/medium monitors.

Here are some pics:

[JLM]

Angled is good, but you'll be hard pressed to find much performance information on non-rectangular rooms.

Equal width/length is bad, the echo based on the length of the room will be doubled based on the equal width of the room. 

Cardas recommends following a 1 x 1.61 x 2.62 ratio which falls within the recommendations compiled by Floyd Toole in his book "Sound Reproductions".  That's the dimensions I followed and am well pleased.

But acoustic isolation of the room from the is just as critical in a family setting.

[FullRangeMan]

This may help:
http://www.audiocircle.com/index.php?topic=107352.msg1183456#msg1183456

[youngho]

Symmetry is generally desirable for stereo listening.

[coke]

If you're putting a toilet in the room, you should at least turn it so that it faces the speakers. 

[Big Red Machine]

Splayed walls are usually intended to be widening toward the back of the room, not the front of the room. In a concert hall, they typically get wider away from the stage. So I would switch my seating to the other side of the room.

[Hipper]

Would there be any sense in having walls angled off the vertical (for example, so the width of the floor is 400 cm and the width of the ceiling 420cm)?