Galvanized C Purlin span question

You get what you pay for for free. Hire an engineer.

You need to calculate dead, wind, snow, and live loads per your local code or IBC code. Then design the beam using AISI S100 code (insanely complicated) or a free online program. I don't think anybody can give generic or free advice on this kind of thing, it takes time to calculate.

If you need a place to start, about 6' for the first span and 6' for the second span is in reasonable territory. That doesn't sound like much; that's because I didn't run a calculation and I don't want the thing to collapse and kill someone because of a random comment I made on this forum, but I know it'll work.

I don't know which option you should use, they're both very similar in strength and you can't know until you calculate it.