[builtinbkyn2]

Hinge a center section of 7' from to back using a piano hinge as suggested by Steve. The two side wings (triangular pieces) would be fixed. There's no other way to have it open from the top, if that's what you want, as it gets narrower toward the window.

 

[builtinbkyn2]

It can absolutely be done. I can actually visualize the mechanics for one method in my head. A couple T-tracks on the bottom of the top and then a T with a cylindrical top or a notched out end of the track to allow it to pivot when fully extended would do the trick. Hidden pocket cabinet drawers do something similar.

Problem is I have no idea what the name of those parts would be to search for.

There are always a million ways to skin a cat, but this would be how most would do it. Because the span is 7', you will need support framing under the seat. 2x3s would be fine.

 

[builtinbkyn2]

Built some beds for my boys a long time ago, the plywood top had a cut out for storage. Just a finger hole and rim to hold it up. Mattress held it down. Never even used it!!

Where can you buy 2x3's? This isn't England.

Well I guess they call them 3 be 2's.

Oh, I get it..................

Any big box store has 2x3s.

 

[builtinbkyn2]

Whaaaa??? Where? In Brooklyn, not here 😁😁😁

LOL well the link I sent is to the Wilkins store here near Pittsburgh. But yes, they have them in Brooklyn too. Where's "here" that's lacking normal building materials?

 

[builtinbkyn2]

The Free State of Florida! 🇺🇸

A lot of New York snowbirds are probably wondering why there are no 2x3s in Florida

 

[builtinbkyn2]

I think I know why there’s a dearth of 2x3s in the sunshine state…………….no basements. They’re usually used as a “space saver”. Basements don’t have load bearing walls and can save a few inches in a room. HD and Lowes probably did their due diligence on this lol