The barn, if constructed properly and maintained, should have no problem lasting 20+ yrs.   We're using a barn much much older than that but it has had lots of work done to it over the years.

The equipment will all have varying lifespans.   Auger and fan motors will start going bad after about yr 2-3.   They just do, for no real reason other than being in a bad environment.    The gates could last 20 yrs with minimal fixing or they could be complete junk after 10 yrs.  The difference between good gates and junk comes down to the feet and the welds.  Ideally the feet should be stainless and several inches tall before switching to mild.   Its hard to see a bad weld vs a good weld after the gate has been dipped in paint, ask around.

If you're custom feeding theres a decent chance that when your first contract runs out you will be told (in order to get a new contract) you will either take less money or you have to put in the latest/greatest new feeders even though your feeders still look like brand new.    Its happened a lot around here, I've bought some of the not very old used feeders for very little money compared to what they cost new.   New feeders currently cost somewhere around $8/space.  The 5-7 yr old feeders sell for little more than scrap because theres a pile of them out there all because somebody wants the latest/greatest.

I don't blame them, it doesn't cost them anything, it costs barn owner.

The comment about working for free is just that in order to have the barn pay for itself in 10 yrs you will get to take NOTHING out.  Equity is good but you can't put it on the table for your family to eat.

Don't put too much value on the manure to make the cashflow work.    I see this as a trap that is coming.   Lots of N production is either being built or in the planning stages.  I really believe that in the near future commercial N could be coming down all the while diesel fuel and the cost of applying manure will continue to go up.

I wouldn't look for custom feeding rates to ever go up much either.   As long as they can find a steady supply of people willing to build new barns theres no reason to pay more.   If anything they'll go down whenever the industry gets in a bind moneywise, which happens every few yrs because of the never ending expansion.

The guys saying it worked great 10 yrs ago are looking in the rearview.   It would've worked even better 10 yrs ago to have stuck that money into land and done less work, again that's looking in the rearview.    You need to look forward.

As always when these threads come up, I'd suggest you work in someone elses barn for a while (without being paid would make it realistic) to get an idea whether you want to be married to a hog barn for the foreseeable future.