Its about the right size / type / condition for the property I would like to find to upgrade from the duplex I sold in 2019,   and from my research,  it is likely that the ownership are getting to the point in their tenure where selling might be on their minds.Given the building's likely income/expense numbers  (I own a nearby, similar style/quality property I can extrapolate from) I can make an educated guess to its value and given that value range I can afford it without excess leverage.   

It seems that the greatest factor in the quality of the deal is not the cost to acquire the property but the rent on the units. 

Dwelling (Building coverage)The limit should be based on the Replacement Cost of the building (cost to rebuild withthe same kind and quality excluding the foundation)2.

The repayment terms for a 401k participant loan are equal monthly/quarterly payments of principal and interest (typically prime plus 1%) over a 5 year term (longer if used to acquire your principal residence).Please note that if you take a full $50,000 and then pay back the loan, you can't take another $50,000 until 12 months after the first loan was fully paid back.Per the loan offset rules that went into effect with the 2018 Tax and Job Act: if you leave your job and the loan is current at the time you leave your job but then the loan goes into default because you left your job, you will have until your tax return deadline (including any timely filed extension) to make the loan current by depositing the outstanding balance into an IRA (and thereby avoid the taxes and penalties that would otherwise apply).Please keep in mind the multiple loan rules:Under those rules, the sum of the balances of a participant's outstanding 401k loans under a single 401k plan (using the highest outstanding balance of each loan over the last 12 months) can't exceed 50% or $50,000 whichever is less.

@Christopher Dolan ultimately that decision is up to you, but I would start by conducting a survey of all other rentals on the market and figure out where your rental fits in based on condition, quality and location. 

Even the nice ones are of lower quality and there is a stigma attached to them.Other than that, it's difficult to answer the question without knowing your market.

But to counter my own point, a lot of customer decision comes from location, your interior design choices, reputation and photo quality.

If the shed adds value compared to other homes of comparable location, quality, and size, then I would bump the rent $50 - $100 depending on the price of comparably storage units in the area.

With a commercial property, @David Beasley, the lender cares much more about he quality of the deal and your experience as an operator.

@John Redman the LL responsibility for the quality of drinking water varies by state.