weight bearing ability of home made truss

It will support exactly what is on the certificate of compliance, and the person who signed the certificate say it will support.

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I know you want a simple number, but such a thing is simply not possible.

You really are asking the question backwards. The question should be, 'I need to support, this stuff, will two pieces of 2" x 12" Pine lumber, with 3/4 ply allow me to do it.'

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I can come up with an endless list of things that need to be considered, including, but not limited to: is it,

Indoor or Outdoor?

Fastened together in any way (If yes, how?)

What is holding the truss up?

Spanning any distance?

A dynamic or static load?

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It is kind of like asking, 'How much will my wife let me spend on tools if I want a drill and a circular saw?'

If she is the AHJ, you can only spend as much as she allows, sucks, but such is life.