Every single sharp point and angle in there will be a stress raiser and possible crack initiation site. They ought to all be changed to include a radius instead. But yeah, with regards the rotor itself, probably worth just buying a Gusset R-Series and being done with it... My guess is that if you made that you'd end up with a distorted disc likely to crack when used for a prolonged period. No reason not to go for a tensioner, brake lever, booster, bashring etc though.