Measurements - Need some help

[Fonte Boa]

I would create one N "leg" with the wanted width (4 wu in your example).
Then i would duplicate it twice.
Finally, i would rotate the middle one and use on its longer edges
the command Intersect so that they will grow until reach the other two legs
(using Edges|rmb Intersect two times).

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I've recorded a short video, not worrying about accurace, showing the method.
After rotate intermediate "leg", i used Edge|rmb Intersect twice,
and to extend the other "leg" edges to coincid with the intermediate ones
i used Edge|mmb Intersect (then, i pointed first the Plane and then the Point, before execute).