At that size you will need to consider specialty materials, and having significant gain will be paramount to being absolutely mandatory.
There are not a lot of choices, and virtually none are affordable in the true DIY sense.
If you throttle back one dimension to 9', then there is Black Out Cloth to consider. It can then receive a high gain coating.
But in retrospect...the w1080st simply does not have the horsepower to perform adequately on a 245" diagonal screen unless the surface used is at least 2.0 gain....minimum.
Lets refine the info.
1. Is this 10 x 20 monster supposed to show 16:9 or 4:3 formatting? I can see something happening at 2.35:1 (100" x 240" *260" diagonal) but only if you achieve at least 2.0 gain and have adequately controlled lighting.
2. Are you intending to try to fill as much "screen acreage" as possible?
3. Are you wanting to view imagery with any light on whatsoever?
4. Are you flexible as to your PJ's positioning? You would absolutely have to place it within 5% of the shortest throw possible.
I know of a few commercially available Screen coatings that go up beyond 3.0 gain, but they are expensive, volatile mixtures that require great care in the application. To do your size screen would amount to an expenditure of over $1000 on just the paint. (...a very good reason why DIY Screen making using ordinary paints is so popular...
I've made some humongous sized screens, and worked a few impossible solutions out....but there always limitations, be they expense, existing equipment, installation considerations...etc.
but the most daunting issue is almost always the desire to go beyond what is possible. That always has to be mitigated with a dose of reality check.
So pinch your nose, swallow...and let's see what we can accomplish.
Rethink your needs and requirements. You can accomplish much at 180" - 200" diagonal.