Glad the Spandex got to you. Glad to help you out too. Over the years I've often heard the laments from AVS'ers living in the Mideast and Far east whose requests to ship simple things are denied by Vendors. It's really a simple thing to acquire such things and reship via the USPS system when spare time allows for it. But an insurmountable hurdle for those outside the US.
Fame, eh? Wood is the way to go.
For a 120" x 68" er your going to need two 12'
2x4's and four 8' 2x4's. The 12'ers must be carefully hand picked and examined for straightness and any degree of twist. Ditto with the 8'ers.
Do you know what a "Miter Cut" is? It is the preferable way to join a corner and achieve a correct angle by matching up the angled edges. The alternative is a "Butt Corner", where the flat edge (must be completely square on the end) is set against the end of the opposing piece, the corner angle checked with a Framing Square (2' x 2' is best), and Wood or Steel Braces applied across the corners. 1/3rd of the way in from each end you place a 2x4 vertical brace that helps straighten any 'end to end' bowing and prevent any twisting in the future.
can be used as Corner Braces...and "Pyramids"
at each junction of the Vertical Center Braces and the horizontal Top and Bottom pieces. Fortunately, even a tightly stretched Spandex screen does not impart undue stress on a wood frame...nothing remotely as much as Black out Cloth or actual Mfg Screen material.
If you plan to have a surround of Black Trim, then no "Stand-off" edging will be required to prevent Frame "Bleed Through". The Frame is constructed so that the 1.5" "Edge" of the 2x4's faces outward, and the inside "Vertical Braces" lie flat from top to bottom, and are flat / flush to the "Rear" edges of the Frame.
Using wood allows you to simply staple the Spandex...and 2x4 wood should be easily enough acquired in India. Using Metal will require special attachment hardware, and unless you have a special Mill that makes such sizes, I don't think you'll find any 10' x 6' sheets of plywood. In any case, such a build would not be prone to "Not" warping" so I'd wholly avoid that suggestion.
I'm on the East Coast at present and cannot post up the simple diagrams of both methods you might find useful until next Monday. I wish it could be sooner, but.......
Can anyone else on here take up the slack?