Apartments just seem to really catch my interest more than the other methods that I have seen.

Two other methods I can think of are subject to and seller financing for creative financing.

With your method of paying off the properties it would be foolish to keep them once they are paid off as their cash value wisely invested elsewhere, in a truly passive form at retirement, will far exceed any income the properties themselves generate.Rental properties can not be considered as a passive investment by any stretch of the imagination.

That method is much more applicable to real estate that is used purely for investing - i.e. commercial or multi-unit real estate.

In the end, like many people, I would love to achieve financial independence by investing in real estate using the passive income method.   

Some owners prefer this method of funding projects. 

I currently build new homes for a living, but I am very interested in getting into FnF, buy and hold, and BRRR methods.

good concept Bryan, flipping vs buy and hold are keys to how wealth can be generated by using two different methods of investing aka envesting as i like to say, i'm a newbie in this industry my plan is to buy and hold rentals and later refinance the property and reap the benefits of the cash flow to purchase rehab and flip discounted properties that i find along the way, my strategy may be different than most but most of my educational coaching suggested looking at every deal as if it were flip and or rehab, i agree with Bryan, if i can get the cash flow and equity that buy and hold offers then that is the strategy that works best for me, but if i run across a flip/rehab that is worth my while then i execute accordingly but leverage is a important aspect of the buy and hold strategy will be implementing in my world.......good luck on your investing journey

Was hoping to avoid the traditional check method.

If they cant sell it via traditional methods they will be more willing to negotiate with you.