Potatoes and carrots should chopped to be between 1 - 2 inch cubes, onion slices should be 1 inch slices and mushrooms halved or quarters.
If using fresh herbs finely chop herbs.
On large cookie sheet spread out vegetables into single layer. Well coat vegetables with olive oil and then toss with herbs and seasonings. Add more oil or herbs if vegetables seem dry or are not well coated.
Place in middle rack of oven for 30 - 40 minutes. Toss vegetables at least once while cooking to prevent burning.