Hello David,

There are a number of "truss types" that could be applicable to your scenario...yet without a rough plan or even basic plan view/elevation view concept it is difficult to impossible to suggest one.

Metal fasteners changes nothing...and has no effect, for the most part...in strengthening a splice to the point of not still requiring other support. Now, with the correct adhesives and scarf joint you may improve strength considerably yet that does not change the "thinness" of the beam which is concerning without proper design. I can think of a few Asian systems that have such thinness. "Tidewater Capes" and few other timber frame styles also have beams in this size range..

If this is a 53° pitch that suggest a "3,4,5" classic roof style pitch or what is called 合掌 (Gassho) or "praying hands" pitch. If the walls are not already built (or even if they are add the height needed) I would suggest rafter ties anyway so there is better utilization of space even if only a half loft. "Collar Ties" from a structural perspective do little for a frames strength, and in most high tectonic or wind events...can weaken the roof by causing a "hinge effect."

Hmmm....I am not sure how a conclusion of 'roof weight' was reached without some actual engineering done? You have live and dead load to consider, as well as, dynamic wind loads. Thatch is not "lightweight" when done well in most traditions, unless this one of the 'tropical' modalities in hanging the thatch.

There is much to consider on this project, even if it is diminutive in size. From proper rafter spacing to actual design overall. This further suggest guidance and submitting an actual drawing here for feedback. If you can't load drawings here, post a link to them...

Regards,

j