Design a wooden truss.

I am planning to build a studio apartment over my garage and want to use exposed wooden trusses to support the roof. The trusses will be the main architectural feature. See attached photos. The trusses must span 30', be 4' on center & support a total load of 50 PSF. All members of the truss shall be made of 1" X 6" lumber (True dimensions = 0.75" X 5.5") Bearing entirely on the top chord. Top & bottom chords shall be double members (made of Batu - Google the properties) that sandwich the single member diagonals (made of Oak, Alder or a similar light colored wood) much as shown in the attached photos of a model I built. The overall look I want is very similar to the other attached photo except I want the contrasting light wood/dark wood theme of the model. The use of Batu on the top & bottom chords is a requirement. The diagonals can be of a suitable light colored wood with sufficient strength. As the maximum length of available Batu is 20', there must be at least one joint in both the top & bottom chords