How long the veg will take depends on how thickly or thinly you have sliced them, and of course how hot your oven is. I find that around 35-40 minutes is enough for a 180C/350F oven with the vegetables sliced fairly thickly. This should give a soft and caramelised result. You can roast them in as little as 20 minutes if you prefer a firmer result and increase the heat of the oven to 200C/400F. You may need to slice them a little thinner to make sure that they are cooked.