what roller are you using - brand / nap??
what condition were the walls and were they primed? If so, with what and was the primer tinted??
Red is pretty much the hardest color to paint with. When using dark reds is standard operating procedure to use a high quality paint (like BM's Aura), use a good roller - purdy or similar, and plan on doing two coats. If you use something other than Aura or similar product, plan on using a tinted high quality primer. Two schools of thought with the primer under reds - some like a gray primer and some like a red primer - either way with most brands/lines of paint you need a tinted primer first.
I'll warn you now - if you answer Behr / valspar / or similar brand of paint - the collective sigh from the people on this message board will be heard from miles away =)
1/2" nap for sure. keep a wet edge, don't press too hard, expect to use multiple coats. if you did buy valspar you better have an airless to shoot it on with. if you bought behr give it away. make sure the room is 70-80deg too if you can. it's starting to get so cold out that painting is getting to be much more difficult than it was mid summer.