As I mention in the headnotes, this method works with all large, red-meat roasts, so beef, deer, moose, caribou, etc. It is intended for hind-leg roasts you want to eat rare to medium.
Coat the roast with the oil, then massage the salt and spices into it.
If you are using a smoker, get it ready. You want to smoke around 200°F and no hotter than 250°F. Wood choice is up to you. If you are using your oven, set it to 225°F.
Set the roast in the oven or smoker, and insert a probe thermometer into its thickest part. With a roast around this size, you will be shooting for an internal temperature of about 110°F to 120°F. This could take as long as 3 hours to reach, but normally it takes a couple hours.
When you hit that temperature, remove the roast and set it on a cutting board. Remove the probe thermometer. Either increase the heat of your oven to at least 500°F and better yet 550°F, or get a grill or pizza oven roaring. 600°F is not too much heat.
Return the roast to the screaming hot oven or grill (cover the grill if that's what you are using), and roast for 10 to 15 minutes. If you've hit 600°F, you may only need about 6 minutes. You are looking for a pretty, browned crust.
Remove the roast once again and let it set on a cutting board. Re-insert the thermometer, ideally in the same hole. Let this sit until the internal temperature hits at least 127°F, and no hotter than 145°F. In terms of time, no less than 10 minutes and up to 30 minutes is fine. Slice and serve.
Notes
The 5 pounds for the roast is just as an example. See the headnotes for guidance on timing.
Keys to Success
Cooking large roasts is an art, not a science, because there are so many variables in terms of size, temperature and time. If you don't have a probe thermometer, err on undercooking your roast. You can always cook it a bit more.
If time is not an issue, you can drop the smoker temperature to 200°F or lower and get a really nice smoke on the roast before finishing. It's up to you.
The spices I use are just what I like. Use what you want, or skip everything but the salt. You need the salt.
Leftovers make great sandwiches, and are good in steak salads and chopped in tacos, burritos or enchiladas.