30k seems too low, unless this like a 1bd 1ba cabin lol

I have mixed feelings about them as do many seattlites,  but generally speaking they are more organized and better managed than the currently available alternative  (tents,  broken down RV or cars,  or piles of cardboard)   ---   I'd trade a larger tiny house village  for an equal reduction in the number of "unsanctioned" campers in an equal radius of my home  (and investments)  any day.That said,   I do disagree with the "low barrier" ones (which allow drug use/etc). 

From the money side of thing, it makes a lot of sense since its cheap, highly customizable, modern looking and low maintenance cost due to steel frame structures.Once we are done with the first big project this year, the following one will be simple and we plan to do more with right amount of funding. 

Look at home depot, lowes etc and find materials costs.  

Property values may be low but rents are also low and people are buying some pretty tough properties at high valuations right now.

yes, I am looking for rental properties  for long term.I am also thinking like now-a-days properties are all time high, interest rates also not that much low...Should I go ahead or just do private lending for couple of years..until market come down.

First, based upon the size of the house, almost 3,800 sft, I would guess your rehab estimate is low. 

If you are flipping at the top of the market and the property is between 1000-1500 SQFT, retail construction in our area would be anywhere from 35k on the very low end to 60k pending where it is located. 

Work on building systems that will allow you to scale by having other people take over the low value tasks that you're having to do now.2.

If you do it now, you'll lock in a low rate for as long as you have the loan.