The size of a timber truss is an important part of designing a building and while there are no set maximum sizes, there are some best practices. For example, an 8-10 metre span for a timber truss is quite a long one and can lead to problems. Ideally, it is better to subdivide this into a main frame of around 5 metres with a 2.5 metre aisle on each side. This is a way to achieve that 10 metre span that can be desired while still making sure that the roof support system is strong and durable.
There are also different styles of timber roof truss that can be used to achieve the look you want. When you work with a timber frame specialist, you can have this custom designed if you have a specific look you want to achieve while still ensuring that the roof is strong and able to support the roofing materials.