If you add some veg to your roasting tin, like shallots or leeks for example, and also put some liquid in the tray during roasting - plain water is fine, or you could add a bit of wine - and keep topping this up during the roasting, you'll end up with lovely meat juices that you can use instead of gravy.
If you like a thicker gravy, rather than a 'jus' type, take out some of the veg you've used, and as long as it's not too brown/burnt, mash this up and use it as a thickener.
But it will taste lovely without being thickened.