Read our blog post for our advice on staircases and plumbing in lofts - everything you need to know.
Our guide to staircases and plumbing
The way you get into the loft and the detailing of the stairs makes a tremendous difference to the feel and appearance of the conversion. Ideally, the stairs should look as if they are part of the original stairwell, by using similar detailing to that on other floors. Be careful not to use too steep a riser, however, or it will feel as if you are climbing Mt Everest when you go to bed. Straight stairs are less expensive.
Open treads, where you see the side of the tread, look very elegant. Use an architect to draw your stairs and then get help from a stairs specialist, such as Southern Staircases.
I'd strongly advise putting in plumbing and adding an extra bath or shower room on the new floor, especially if the loft is intended as the master bedroom. It keeps the house well-balanced.