How to narrow down the barn builders
1. Compare all the materials each builder uses. Do that from the rough schematics and brochures you just collected up
Once you start reading details, you'd be surprised at how you wouldn't want some of those barns to house a few chickens
2. What is each company using for poles. Same as #1 there can be difference that might literally pull your barn down over time.
3. You should be getting a metal roof regardless of who is building the barn. If anyone says they only use shingles
That's a File 13 right out of your shopping bag. Ask about mil strength on the metal roofing - I'd bet there are some people who might try to use left over SIDING for the roof.
4. Compare pricing on the structure only. The shell of the barn is going to be the same size regardless of who builds it. If you've got a builder with prices "too good to be true", I'd bet they are and you will find yourself with problems down the road.
5. Go on the Internet and see if any of them have any BBB claims against them or just bad reviews in general. One or two might only mean the Buyers were fuss budgets and nothing would make them happy but read between the lines anyway. A handful of bad reviews is a red flag to me.
6. Pick a company that has been in the business several years AND you know for fact can get a semi load of material delivered to your farm<---even if they are buying it from Lowes.
7. Something I would have never done in the past but I sure as heck would do now, is to ask about the work crew. Having been in jail for minor offenses is one thing but do NOT send sex offenders, rapists or murdering thieves to my property. I know they need jobs but some of them are only working construction because of the tawdry opportunities it affords them.
Not quite what you wanted to hear but having had two barns and a workshop built by someone else, in my lifetime, this is my approach. It's going to be your several thousands of dollars and you have every right to ask a lot of sensible questions