Then calculate when you will need that roof and how much it will cost when you do.I do like that high appreciation potential, and this may work well for you.

Quote from @Isuf Aruci: i live in the NY area and would love to build a house or a mid apartment building. but the land search is very very difficult. also lets say i found the land, where would i get information and see if its buildable, also how do you calculate a land to see if its worth building or not.   

Most of their victims are either too naive or too ashamed to do anything about it.

I suspect a legal, permitted garage conversion ADU will cost ~6 times your estimate if hands off and probably at least 4 times your estimate if you do the finishes yourself.  

I am looking to learn more about buying lots and doing infill with modular homes. 

Is it fixed? 

Trying to buy a 3 family that needs some TLC maybe do a BRRR.

There is no differential factor number, however, it will change if you are buying tenant occupied, if they are are going to be vacant at closing, if they are going to stay the full lease or you have to pay cash for keys.

Find the ones that can do it, and it also helps if you have separate contracts for the lease and the option. 

However, it's essential to determine whether they are reputable brokers.