We want to have a single story house built where an attic can be converted into a spare room, recommendations.

Question

We like california bungalows and craftsman style homes. We are permitted to have a 30' wide by 40 ' deep footprint.

Answer 1

talk to the truss company, they will be able to design a truss that will meet your needs

Answer 2

Your resale value will be better if that attic space is large enough to be called a bedroom once it is done.  Check your local codes to see what that size is and what else might be needed like windows and placement of wall sockets and lights.  Some places require a closet too.

Answer 3

One, select a roof structure to allow plenty of attic room for the conversion.  Dutch style roof, elevated a couple of feet.  

Two, make sure the bearing walls, and the floor of the attic will handle the load of the conversion.

Three, make sure you have a space for traditional stairs.  Ummmm leave space so that you can get furniture and plywood up the stairs, etc.  

Four, make sure you have plenty of reserve electrical capacity in your power box, and it would be a good idea to have your electrical plan laid out and the main feed wires in the walls downstairs, etc.  

Route your plumbing vents so they will not have to be moved later.

Insuate the roof structure, so that after the conversion you will have good R - value at the roof.

Plan for the addition of another HVAC unit, for the upstairs.  Duct work, etc.

I'm sure I may have left something out,,,but just go through the process of thinking about load, access, utilities.