Sloped Ceiling Bonus Rooms often present unique challenges. But seldom nothing that cannot be accommodated if one has even a modicum in flexibility and willingness to do what "must" be done.
Probably 75% of all the dozens of Home Theaters I've done over the last 8 years have been sloped Ceiling / Kneewall "Bonus Room" affairs, so I might be able to offer you some insight on what you can do, should do...and what you should either try to avoid, or run screaming the other direction from altogether.
A prudent choice of color for the Sloped Ceilings, one that has as little potential for Screen output reflection as possible is a good start. **
The more consideration given to that particular, the closer you can let the Screen's upper corners crowd the slopes, resulting in the gain of a few extra inches of height off the floor for the bottom of the Screen. In the Bonus Room Theater example shown below, you'll note how close the upper corners of the Screen are to the sloped Ceilings, and that even with a ultra dark Flat Brown paint, that a very small degree of reflection can be seen when viewing a very bright image such as the Supernova Nebula pictured. But at least such a small degree of reflection does not affect the overall quality of the available contrast the projector delivers. (see the second image below taken in a completely darkened room...)An Example of a 110" diagonal DIY Screen in a 14' wide Bonus Room that has Tan Walls and a Dark Brown Shadow area that encloses the Screen wall and adjoining sloped Ceilings. PJ is a Panny 2000
So don't cry....there is potential for great things ahead!
Your desire for a 106" -wide" 120" diagonal screen in a 14' wide (floor width) room is definitely a factor in your needing to mount the Screen so low. While this won't be so terrible a thing for anyone viewing from a single row of seats, the sheer height of the back of such seating will block the lower area of the screen from view if someone is standing back further than 6' from the single row of seating.
That being said, either you need to scale back to a 100" Diagonal Screen (85" wide) and collapse your viewing distance so as to make the smaller screen present the same viewing aspect of the larger screen, or accept the fact that viewing content from the seats is an activity that is removed from doing so further back in the room.
The construction of a 12" high Riser can afford you the potential of adding a second row of seats (...something many if not most dedicated Theaters posses...) Opting for the smaller screen, and therein being able to raise the height of it's placement also serves to allow for such.
Sound. Well, although you didn't mention it, making a good choice as far as speakers, and arranging speaker placement is absolutely critical in such spaces, because frankly, they are terrible as far as acoustic considerations.
PJ choice & placement is also critical due to the shape of the Room / Screen wall, and proximity of the Sloped Ceilings. You need to place the PJ within 10% of it's minimum Throw distance, and as high onto the ceiling as possible. This means selecting a PJ with considerable Lens Shift capability, or one that has at least 14" of image offset. The latter will however require that you mount the Screen to a specific height to accommodate that preordained limitation.
Absolutely you'll need to consider a High Contrast Gray Screen to offset room reflections and to assist in improving Contrast (8350) or allow the selection of a PJ like the 5010 and let it cruise along on Low Lamp mode for the duration.
Is the room still under full construction with Stud Walls open? Any thought given so far to location of the A/V equipment?
Lots to consider...and while for some of us the obvious answers might seem almost intuitive and simple, making such decisions fall squarely on you, and you schedule, budget, willingness to consider alternatives to preset ideas, and above all else, a goodly helping of patience should you decide to elicit several opinions.
That's it for now....more input as to you actual needs, wants, desires, and expectations is needed to really hone in on a definite route to take.
You may PM me for specific and detailed advice on any aspect of your build, and then weigh my responses against others you'll get. This being a Forum dedicated to projectors, waxing too prolific on the entire Build process might grate a bit on some.
Feel free to post up a dedicated Thread here. We can help you on all points. http://www.avsforum.com/avs-vb/forum...rune=365&f=110
But in closing, let me state that if the budget can stand it, opt for the 5010, and don't be reluctant to instead go for the 8350, as the savings you'd realize between the two by going for the 8350 will allow you all the more leeway for any unexpected but absolutely necessary decisions (...and expenditures...) that are bound to surface....soon.