I wanted 12k/month passive income to help supplement my retirement when I turn 65.

My letter is generic, non-personal, fill in the blank.

I use a generic letter.

Be careful not to use a generic form or something you find off google because every state, and often even each city has specific laws you may need to follow in regards to applications.

My primary intention is to slowly accumulate rental properties to supplement my income and maybe, some day, be able to retire early.

Metal roof is fairly generic and can cover a variety of roofs - brass, bronze, copper, iron, steel, aluminium, etc.Around here a metal roof from the 1940s would most probably be a {corrugated} galvanized steel roof.  

No complaints so far but I’ve been supplementing with YouTube videos from prep-agent.

Next year you can join AARP, LOL.Your SSI can have supplemental income earned, but limited before your benefits are reduced.

The course is self paced and mostly text based, so I supplemented it with listening to Travis Everette's lectures of Youtube (highly recommend) and was able to pass both sections on my first try!

Here is a list of a few that I find to be of most value:Population TotalHome ValuesHousehold IncomesPoverty RatePopulation AgeRental Vacancy Rate*Homeowner Vacancy Rate*Educational Attainment Rate (High School/GED & Bachelors)Number of Housing UnitRent to Income Ratio*Rent to Price Ratio*Population on SNAPS (supplemental nutrition assistance program) percentageProperty Tax Rate*Median Age of BuildingsNumber of Structures by Units (SFR, Duplex, Triplex, Quadplex, etc...)Median Rents by Number of BedroomsPopulation Change (Births, Deaths, In-Migrations, Immigrants)  *note that some of the metrics are composites that are computed by comparing two or more variables from the ACSA number of the variables above can also be broken up into cohorts, which will give you even more insight into how an area is doing.