Roasts make wonderful special-occasion meals. Yet they are difficult to get right. Ovens all cook very differently. Cooking times change if more than one item is in the oven and also if the oven is not perfectly clean.
The only reliable way to get consistently good results when roasting meats is to use a good quality meat thermometer. Some of them even have remote readouts, so you don't have to open the oven.
Below are the roasting times recommended by the US Department of Agriculture for various meats. Two things to note:
1 The USDA's job is to make sure you don't get sick. They don't care if your food tastes good or is as dry as shoe leather.
2 The internal temperature of your roast will continue to rise after you take it out of the oven. If you get the perfect temperature while in the oven, by the time you serve it, it will be a dry hunk of animal, which shouldn't have had to give up its life to create such a lousy meal. For example, a beef roast cooked for say 2 hours, can increase its internal temp by 10-12 degrees once it leaves the oven. So, adjust these times and build your own table, based on you preferences.
BEEF, VEAL,LAMB
medium rare--145-degrees (probably 10-degrees to high)
medium--160-degrees
well done--170-degrees (don't even bother, just eat the carpet)
FRESH PORK
medium rare--USDA says don't do this but many people like 
x their pork around 155-degrees
x their pork around 155-degreesmedium--160-degrees
well done 170-degrees
POULTRY
ground chicken, turkey--160-degrees
whole chicken, turkey--180-degrees
breasts-170-degrees ( you will need lots of mayonaise to moisten this thing up).
STUFFING--165-degrees
Egg dishes, casseroles--160-degrees
