Roof Design for Shipping Container Building

[Steve961]

I am in the planning stages of a shipping container storage building. One of the more difficult things so far has been the design of the roof. I am trying to come up with something more akin to a pole barn type metal roof, since it really only has to provide some shade and weather protection. I have come up with my own design, but others that have seen it so far are not so sure it is appropriate.

The specs are:

- 20'x24' building (3 - 20' containers side by side), rafters span the 20' length
- 50 psf live load for snow
- 29 gauge steel roofing
- 4"x8" (dual 2"x8" lumber, No.2 or better) rafters at 4' OC
- birdsmouth cut rafters connected to dual 2"x8" top plates with structural connectors (USP ANJ44S) and 4 - 1/2"x2" lag screws
- 1/2" plywood gussets on both sides of rafters
- 2"x4" purlins laid flat at 24" OC
- 2"x8" top plates connected to shipping container box beams with lag bolts

I have been told by others that I should use a ridge beam, use 4x10 (dual 2x10) rafters, supports under the rafters, etc. The beam span info I have found indicate that dual 2x8 rafters should span 10'. I would also rather not use a ridge beam, and I really don't think it is necessary since the shipping container roofs act as rafter ties.

Any thoughts on this?


Thanks.

Steve