I am 5 10 or 5 11 with an inseam of about 85 or 86 cm. I just got a 58 frame (c-t) and my dad has every part to build a bike for me. my only concern is that he is taller than me, and the cranks he has for me are 175. is that okay for my size?

Yep,

Should work fine. I am 5'11" and have bikes with both 170 and 175 cranks and neither causes a problem.

.........and the cranks he has for me are 175. is that okay for my size?

http://www.cptips.com/crnklth.htm

Not sure if this is possible but probably the only option to proper sizing. What say ye!

http://www.cptips.com/crnklth.htm

Not sure if I totally agree with this site. I ride a 57cm toptube frame, I'm 6'1", and have a long inseam @ 34". I ride 175mm cranks and they work just fine for me, be it grinding up a hill at 60rpm or sprinting at 120.

Not sure if this is possible but probably the only option to proper sizing. What say ye!

if there is not a very significant difference in leg length, you might try the Lemond Lewedge, ( http://www.lemondfitness.com/products/lewedge/ ) or ski shops offer shims that can be adapted to cleats....also see the URL for permanent drilling of crank arm to shorten: http://www.myra-simon.com/bike/cranks.html

Not sure if I totally agree with this site. I ride a 57cm toptube frame, I'm 6'1", and have a long inseam @ 34". I ride 175mm cranks and they work just fine for me, be it grinding up a hill at 60rpm or sprinting at 120.

to your comment..I ride a (custom) 55.5cm top tube, 5'-8" and 30" inseam and ride 170 cranks, but my spinning class only has 175 cranks which are not noticable.. I believe we all adapt, and I think the only way to tell any real differences is to ride the same routes over a length of time (~ 500 miles) with different lengths and see if your body finds better performance/comfort with a particular crank length... it's all relative
(you may find grinding up a hill at 70 rpm better for the knees' health and less burn)