I was hoping for some advice. We will be building a new house soon and I was wondering if I could manage to put in a passable home theatre. We don't have the space for a dedicated room, so what I'm thinking of is something like this.

We have a lounge room/rumpus that will be 5.7m wide by 4.8m long, however 1.2m of the width is an extension of the hallway. On the other side of the room will be a pretty big window – 3.2m wide and 1.5m high. The ceiling will be 3m, so I was thinking we could drop the ceiling 15-20cm for most of the lounge part of the room, except for 15-20cm around the edges. This would create a recess to hide a screen, that could come down for use with a projector, at one end. And then on the two sides it could hide runners for curtains which could be pulled shut for when we watch movies. The curtains would partition off the hallway section. So basically create a room 4.8m long and 4.3m wide. I know curtains won't block sounds to the rest of the house but hope the sound within would be OK.

What do people think? Does I make sense? Does it sound like a good idea?

The obvious solution is to put in a permanent wall, but the hallway is already quite long, and leaving the gap between the "hallway" and "lounge" makes the room feel bigger and more open.

maybe post upa picture.. or the room or just your plans so we can see what it looks like...

It depends on your expectations.

Depth tends to be more the problem than width, and I wish my room were 0.5M longer.

If you want a flat panel display, you will be fine.

My theater room is 7M long, and I can only go with about a 3M wide projection screen at a 2.35:1 aspect ratio (with two rows of seating).

if you only have 1 row of seating, or are looking at a large flat panel - say 60-65inch, then you will have plenty of space.