don't do that. :x the outer edges of the brush won't match the curve. then you'll have to manually resize it.
what i do is first make the sloped brush whatever size, but being on large grid makes it simpler.
then i skew the edge so that the inner part matches the curve:
http://necros.slipgateconstruct.com/temp/ed8.jpg
then, i extrude the face outwards so it goes far past where it should end:
http://necros.slipgateconstruct.com/temp/ed9.jpg
with the clipper, i just lop the extra parts off, by following the same line as the curve itself:
http://necros.slipgateconstruct.com/temp/ed10.jpg
to complete the curve, i take the bit i just made, copy it, rotate and mirror it so it fits on the bottom part.
then, i copy the same part, and skew it so that the inner edges match (just like before) but now the leading vertices will be fucked up, so i just grab those and put them where the previously placed vertices (from the first 2 sloped brushes) are.
http://necros.slipgateconstruct.com/temp/ed11.jpg
this took me about 10 seconds? 20 maybe.