Date: 5/20/2008 3:25 pm EDT
You don't say how big this area is and that information would be helpful.
Installing tile is sometimes more a matter of aesthetics than it is mathematical absolutes. Just for fun lets say you want the tile installation to be perfectly centered in the room.
You use two walls, let's call the longest wall the "primary wall" and the shorter wall the "secondary wall".
For example: You could find the center of the room by measuring from both ends of a single wall (primary wall) and striking a center-line using a chalk box to arrive at your "primary line". Remember (use the longest wall to do this). You would then measure the length along that chalk line and divide by 2 to find the secondary center-point.
Then using that number measure the secondary wall from both ends as you did the first wall. Now snap a second chalk line onto the floor.
You now have a chalk cross marked on the floor but of course you still aren't square at this point.
Now measure from the center of the cross down one chalk line exactly 3 linear feet and make a mark. Then measure from that same center point along the second (perpendicular) chalk line and this time make a mark at 4 linear feet from the same center.
Measure from new mark to new mark and you should have exactly 5 feet distance if your layout is square. If your layout (room) isn't square then of course you will have to adjust your marks using this "3-4-5" until this system works as it should.
You have probably guessed by now this system is known as the "3-4-5-Method" of squaring a room. It works every time and really isn't as complicated as it sounds but it can only be accomplished through trial and error measuring until you get the balance you need. It will be easier to see which direction you must tweak your lines to achieve perfection.
Once you have that information on the floor snap together several tiles to make a large square and match two perpendicular edges to your final chalk lines. Your tile layout is now "square" regardless of the shape of the room and any irregularities would then be cut-to-the-walls when installing the last wall tiles.