D.I.Y Dish tool
 

I don't have a lot of wheel building under my belt, and don't plan on being high volume, so the Minoura FT-1 seemed like a good value. It's a little shaky but usable with care.

The dish gage that came with it is another story, I just couldn't get the correct angle and depth.

Might just be me or the wheel I'm using it on, so I came up with an alternative.






https://cimg8.ibsrv.net/gimg/bikefor...6c6df22e6f.png






https://cimg1.ibsrv.net/gimg/bikefor...370d93afa1.png






https://cimg7.ibsrv.net/gimg/bikefor...2736948ffa.png

No disrespect but I would rather use the truing stand and flip flop the wheel until you get good understanding of the built in side to side error.

The stand works well enough, but the OP’s solution also looks perfectly serviceable, and probably used parts on hand.

Pretty easy to put the wheel on the bike and measure the distance from the stays.

I've purposely off centered rear wheels with disc brakes to get a more equal spoke angle.

If you build more than a few wheels the handy convenience of Roger's design is hard to beat: https://www.wheelpro.co.uk/support/dishing-tool.php
His book on wheel building is outstanding.

Wow, that link sent me down a rabbit hole, looks like a Wheel Fanatyk Tensiometer is on my wish list.

Your Unistrut is much better than the old bed frame I used.

You can also use three stacks of books.

Francis Bollag suggested this DIY dishing gauge a while back. It consists of a flat table, 3 or 6 tuna fish cans, and a stack of pennies. Support the wheel by the rim at 3 points by the tuna fish cans. Two cans should be sufficient so that the axle is above the table surface. Use the stack of pennies as your measuring gauge to the locknut. Flip the wheel. Adjust the dish so that you are a penny width between the two sides.