what temperature should I roast veggies at?

425 for carrots and parsnips, but maybe 400 for the onions if they are sliced because they might burn.

I tend toward 425 to 450 for most vegetables.

For hard veg, I like to start out at 350 for 15-20 minutes and then crank the oven up to 475 to get them to caramelize a bit on the outside. Just be very careful to keep an eye on them at that temp (I set the fire alarm off...twice...last time...).

It's my understanding you can roast vegetables slow up to 325°F, or a fast as high as 500°F. The oven temperature will depend on the type of vegetable. Slow roasting works especially well with carrots or other root vegetables. Many vegetables are easily adapted to a range of temperatures--experiment.