if my dl is 27.5 hat do you think a good arrow length would be?

At least long enough that you don't draw it off the rest at full draw, but I'd stay around 27" anyway. A longer shaft is slightly more stabile in flight than a short one.

A general rule is 1 inch past the riser at full draw.

I agree with BGfisher, I would cut them somewhere around 27 in most cases your arrows end up about 1" to 1/2" less than your draw length.

It also depends on your rest that you use also...

I have a 29" draw length and my arrows are 29 1/4" I can go 29" but the guy cut them an extra 1/4". No biggie...