The two main ways of bearing the roof weight are either supporting it with the walls, or using posts and beams to hold the roof up and filling in between and around them with insulating, and/or massive material. Both systems have their advantages and disadvantages:
Post and beam:
*Same standard design can be used with many different in-fill materials, allowing different walls to be filled differently without regard to structural integrity.
*The roof can be put on before the walls are up, giving shade and protection from rain
Load -bearing walls:
*Less wood required
*Stronger/simpler corners on stone and cob walls
*A natural for earthbags
In most of our lightweight, quick to build structures, we use the post and beam method, as it allows us to get a good feel for the structure (size, location, shape, etc) at the beginning, Then the rest of the construction can progress naturally as the walls are in-filled with a variety of materials, with doors and windows moved around easily too.