Best to talk with your uncle and grandpa, get a materials list and take it to a good independant lumber yard (not big box), Some will even do the materials list for you if you take in pictures and measurements.
True. When you get to the point of considering a fire escape, this is one alternative. Again, check what is allowable in your area.4. Stair is not necessary, although it could be handy fire escape. Stairs can take up a lot of room in your yard. A landing in the middle takes more material.