1. Follow the "rule of 7s": Enforcement varies, but codes typically say that at least half of a finished attic must be at least 7 feet high, and that this area must be a minimum of 7 feet wide and 70 square feet. A contractor or town building official can help you assess how the rule will apply to your attic and how modifications like dormers can resolve height shortcomings 
2. Have an engineer check the structure.  A finished attic weighs a lot more than boxes of holiday decorations. Have your home's foundation and framing inspected to ensure they can carry the extra load. At a minimum, you may need to strengthen the attic's floor joists, which are often too shallow or spaced too far apart.
3. Consider your access. If you're building a staircase from scratch, consider a switchback layout. It needs more room than a straight run (roughly 45 to 50 square feet per floor versus 33), but its footprint is more square than linear, so it will often fit in spaces where a straight run can't go. Just make sure the landing is large enough to maneuver furniture upstairs

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