I have re-roofed hutches before. Depending on how big the hutch is and its construction, I have put a suggested shopping list together from Wickes as it was easy to find (discounts often available if you order online). Timber yards will be cheaper. You will need basic tools - drill, drill bits, screwdriver, saw, tape measure, etc. Roofing felt is much easier to handle on a nice warm day as it is flexible without cracking.
If the old roof is too far gone, remove it and replace it. I tend to add a new sheet over the old if possible. That way I can add a bigger overhang without any other alterations (especially at the front so I don't get dripped on) and more of a slope for better drainage (add a batten right across the front - fasten to the hutch with screws, then screw the new roof on top). Materials you might need:
Batten:
http://www.wickes.co.uk/Wickes-Treated-Sawn-38-x-47-x-1800mm/p/9000036485
Screws for batten:
http://www.wickes.co.uk/Wickes-External-Grade-Screws-Green-No-8x50mm-Pack-20/p/156548
Screws for roof sheeting:
http://www.wickes.co.uk/Wickes-External-Grade-Screws-Green-No-6x23mm-Pack-30/p/156544
or
http://www.wickes.co.uk/Wickes-External-Grade-Screws-Green-No-8-x-23mm-Pack-25/p/156546
New roof sheet:
http://www.wickes.co.uk/Wickes-General-Purpose-OSB3-Board-9-x-1200-x-2400mm/p/102972
or:
http://www.wickes.co.uk/Structural-Softwood-Plywood-CE2+-18x1220x2440mm/p/120945 (although you may find some thinner structural ply elsewhere)
Cut the sheet to the size you need, screw on to the battens / old roof via some main parts of the hutch structure, then cover it in roofing felt using large headed zinc nails. If you have an overhang all round, the felt is easier to tuck underneath to make it more waterproof:
http://www.wickes.co.uk/IKO-Green-Mineral-Shed-Felt-10-x-1m/p/164174
http://www.wickes.co.uk/Wickes-General-Purpose-Tacks-16mm-40g/p/516100
or use a suitable stapler (like ones for paper, but more substantial).
I also tend to cover any hutch / shed roof with a corrugated bitumen sheet as it gives much better protection for many years:
http://www.wickes.co.uk/Onduline-Green-Corrugated-Bitumen-Sheet-950-x-2000mm/p/240059
http://www.wickes.co.uk/Wickes-Profile-Sheeting-Nails-70mm-Green-PK20/p/240099
