First, Welcome to the Garage Journal. You have posted in the Gallery which means you owe us some picture rich updates as your project progresses. We like pictures.
As for bolt up or weld up I don't have a good answer. Around here virtually all steel framed buildings are bolt up. The only weld up I am familiar with was in a tread here on the GJ. It was also a Texas build so the practice may be regional.
Has your builder discussed the differences in terms of cost and results with you? I would be interested in knowing what you select and why.