Tedd is speaking wisely. The whole concept is an attractive one....but as such comes with considerable and necessary expense.
Now if you can, and will put all your resources into the "Build" and defray further expenditures for a later date, absolutely you can achieve something spectacular...albeit over the passage of time.
Can you elaborate on what you have in mind when you say a “truly large screen”? I’ve depicted a 150” 2.39:1 screen. The max I could do at that aspect ratio looks to be a 200” screen, but that would almost span the entire width. Even then there would be plenty of height at the low end.
A 16:9 screen could be up to 210” and though it would still fit easily height wise I’m not sure how it would look from the back row. Nevertheless it fits, though I can imagine the large wall would be much more appropriate/optimal.
"Truly Large" in a room the size/length your considering would be 180" and up. And that size is about right. But I'd advise that it be in a Constant Image Height format, and that the width of the Screen be the defining factor.
Such a Room is not a TV room, so a focus on 16:9 formatting would be a grievous error. For that matter....so would 2.39:1 Or IMAX. You need a flexible situation that would not entail excessive expenditure.
If the room is built so that the presentation Wall is at the tallest end, it would be easily done to have the Right /Center / Left Speakers exposed in front of a Painted Screen wall that would allow for ANY Format to be shown in whatever size was desired...and possible according to the Projector's attributes and placement. If the PJ has motorized Lens Shift (and Memory) then when the Theater is packed and the 3rd row full, the image could be sized and positioned to whatever works best.
Another benefit coming from a correctly painted Wall Screen would be the ability to provide enough gain at the Screen's surface to compensate for such large imagery. Acoustic Transparent Screens are NOT going to provide such, requiring those prohibitively expensive, upper echelon PJs just to give you an acceptably dynamic presentation.
I might get Boo'ed for suggesting this but a "budget choice" for such a large Screen would not be a JVC-anything, but rather the Epson 5050. It has sufficient Lumen output to put you on the positive side of things.
JVC NX9 - 2200 Lumen - 18' Throw onto 1.3 gain surface = 25 foot lambert
Epson 5050 - 2600 Lumen - 18' Throw onto 1.3 gain surface = 35 foot lambert (a Big Difference!)
Then there is the sheer cost of any AT Screen in a size at or over 150" diagonal...let alone 180". You'll be checking your pulse after checking the prices of such.
So...taking you professed desire to maintain a tight budget,yet also acknowledging that a project such as yours deserves special consideration, below are images of a rather resplendent Theater (18 seats) that has a 192" x 80" (16' x 6'-8" 208" diag.) 2.39:1 Painted Drywall Screen being serviced by a JVC RS2 (w/just 600 lumen ! ) I painted that screen for a AVS'er back in 2009! So do not even imagine that such performance is not to be had today. And that being the case, the money saved on both the Projector and Screen options will certainly help out in the "Build process".
The following images were all taken with a digital Pocket Camera and have not been altered in any way except Cropping and resizing.
Wide Angle shot
My personal mechanic...............
Achilles and the Boys....
A lot of ambient light (...and two Side Spots...) present for 208" & 600 lumen.......
And below is one of my favorites.....showing how good the Blacks can be with controlled /Directed lighting present...and with the Stars out too!
Keep in mind that an 2.39:1 image of 208"diagonal w/C.H.I. would still allow for a 80" x 142" (163" diag.) 16:9 image, still somewhat larger than most, I'd say.
If you have the DIY work ethic....you could do something very close to the above for $1000s less and I do feel it would be the deserved focal point of your Theater to have such epic imagery
......................on a tight budget too!