Try this...
Cut up the potatoes (peel first if you like), and boil for 5-10 minutes, just long enough for the corners to soften a bit, but not too long. Floury potatoes like King Edwards are good for this.
Drain them, using the lid to keep them in the pan while you pour away the water, and then pour oil onto the spuds in the pan and stir them around to coat with oil and slightly break up the sharp corners.
When you want to roast them (whether straight away or after they have cooled) tip them into a roasting tin and pop them into a pre-heated oven (quite hot - they need to be roasted fairly vigorously, not cooked for a long time, as they are already cooked.) While they are roasting, wash up the boiling pan, so all you have to do after the meal is clean the roasting tin.
A sprinkle of salt and pepper and chopped rosemary before roasting is nice.
Good luck.