How wide is your barn going to be? I really like these metal type of trusses because you can get a nicer roof pitch out of them along with wider width then you can with wood and have the open ceiling. I'm looking into building an event center using trusses like this that will have a 40 foot span. My plan is to set the posts every 8 feet and use 24ft long 2x6's on edge for the purlins. I feel that the extra cost for posts and purlins is minimal compared to the additional strength I will get with this layout.
Armour Metals Measuring & Installing - Metal Roofing and Pole Barns This is a website that has pricing for the trusses. It's farther away then I want to deal with, so I just use it for reference. I still might go all metal for my posts and trusses with Muellers, but have to spend some time talking to them before I decide.
I'm not a fan of slider garage doors because they let water and wind get past them. There are ways to seal them up, but from what I've heard, they don't work very well. Adding a porch roof over the door will help a lot with water, but wind is always going to be an issue. I like roll up doors. I still get a little wind through the edges of mine, but it's never been too bad.
As for spanning trusses, first you have to decide what type of roof do you want? Shingles mean you have to have your trusses 2 feet apart or closer. Higher end homes tend to go 16 or 18 inches on center. Especially if they have a heavier type of roof then shingles. The main reason for this is you attach the shingles to the decking, and either plywood or OSB can only handle a 2 foot span. Shingles also do best at 4:12 pitch or better. Depending on your weather conditions, anything less will result in failure. Metal can be as low as 2:12. If you go lower, you run into issues. Most metal buildings are going to have a roof pitch of 2:12 up to 4:12. You can get steeper, but there is a big jump in cost if you do so.
With a metal R panel type roof, you attach the metal to the purlins. These can be spread out as far a the wood is rated for. Usually a 2x4 on the flat is good for 4 foot spacing, 2x6 on edge is good for 8 foot and 2x8's are good for 12 foot. I've seen 16 foot spans with 2x12s, but mostly they are done with metal purlins. I'm never going to span more then 8 feet in anything I build, so I'm not familiar with all that's involved with the wider spans. I think your builder going ten feet for his spans is at the max limit of what will work, which I don't like to do. I like to be well under the limits because things tend to fail when maxed out.
If you want to spend more money and go with a hidden seam metal roof, then you have to deck the roof the same as a shingle roof.
Most cost effective is going to be R panel metal roof with an 8 foot span between trusses in my opinion. I prefer to have the trusses resting on the posts.