好象屋顶建造很复杂，什么都可以自己建，只是倒水泥建地基和屋顶不行，据RONA介绍，有公司定制屋顶：

With the walls up, you should close the roof as soon as possible to avoid rain or wind damage to the inside of your garage. Roof trusses are a pre-built series of structural members designed to carry the load of the roof to the outside walls. Trusses are built in special factories to the individual specifications for your garage plans.


Trusses are designed to resist loads only when they are in a vertical position. That is why they should not be lifted flat or laid over the top of the outside walls. Gently lift the trusses mechanically or with a rope and pulley

只是不知如何寻找这些公司。