What type is the oven, gas, electric? I assume it is an electric model one. Which mode do you use for roasting Is it convection, or bake?

If you have been using bake. Try convection. Convection will promote drying.

Another option is also to roast at higher temp at shorter timing.

And be sure that your veggies are not crowded in the pan. Leave plenty of room to spread them out.

Most importantly, dry them well before you put them in! Pat them with towels rather than just draining, and leave them sitting out for awhile if you can.

Many of the vegetables that are good to roast have a lot of water in them, so do steam some anyway. Even though caramelization happens at 350° F., boosting the heat to 360° might help. I have a number of recipes that call for that, and I've been pleased with the results. Also, a little (importantly, not a lot but just a little) light oil helps the sugars to brown. Suntan lotion. :) I use "light olive oil", and safflower is great. Corn and peanut oils are heavy. Canola is in the middle. It's the viscosity that seems to matter for this.