In a small bowl, mix the brown sugar, salt, pepper, thyme, rosemary, garlic powder, and onion powder together.
Rub the ribeye roast with olive oil, then evenly coat it with the spice and sugar mixture, pressing gently to help it stick to the meat.
Place the roast on a rack in a roasting pan, fat side up. Insert an oven-safe meat thermometer into the thickest part of the roast. Allow it to rest on the counter for 20-30 minutes to take some of the chill off. While it’s resting, preheat your oven to 425F.
Roast in the preheated oven for 15 minutes to form a crust.
Reduce the oven temperature to 325F, and continue roasting for about 20 minutes per pound for medium-rare, or until desired doneness. For a 4 pound roast, you would bake it at 325F for about 1 hour and 20 minutes, and for a 5 pound roast, you would bake it at 325F for about 1 hour and 40 minutes. For medium-rare the internal temperature will read 130-135F, keeping in mind that it will raise 5-10 degrees after it rests. For medium, allow it to continue cooking until it reaches 140-145F. For other levels of doneness, see notes.* Keep in mind that it is recommended to cook it until it reaches an internal temperature of 145F, but individual preferences vary.
Remove the roast, tent with foil, and let it rest for 20 minutes before slicing.