Preheat oven to 400 degrees. In a large bowl toss together potatoes, carrots with 2 1/2 Tbsp olive oil, thyme, rosemary and season with salt and pepper to taste. Spread onto a rimmed 18 by 13-inch baking sheet. Roast in preheated oven 20 minutes.
Toss green beans in bowl with remaining 1/2 Tbsp olive oil and season lightly with salt. Add to baking sheet with other veggies, add garlic and toss everything and spread into an even layer. Return to oven and roast until all of the veggies are tender and slightly browned, about 20 minutes longer. Serve warm.
Recipe source: Cooking Classy
Try to cut each separate type of veggie about the same size as each other so they roast evenly.