Wheelbuilding / Wheel Building / Wheel build help

I’m assuming normal race spokes at a quarter of the price will work especially if you file down 1 side

If you mean making your own flathead (t-head) spokes out of normal straightpull spokes, you could use Damon Rinard´s method:

Just squeeze a straight pull spoke in a smooth jawed vise, Just include the first ~20mm of spoke wire in the vise too, then it automatically stops. A shop vise can't possibly provide too much pressure

I would not recommend filing spoke heads