ADVISE PLEASE!! HOLD, BUILD, REFINANCE?

[Karina Segovia]

HI 

I purchased a home in a multi unit (R4), high density zone.

I am currently renting the house cash flow is just $50 after mortgage payment.

This house has a big workshop in the back with a high rise ceiling, brand new roof, electricity and water.

It sets in a half an acre lot so I am able to rent the workshop and land for $700 a month 

Total cash flow on this property is $750 a month

I'd like to enclosed this workshop (it has 3 brick walls already built) and make it into a livable place.

I can still rent the land and keep the cash flow at about the same amount ($700).

However there's no sewer  at this house just 2 septic tanks attached to the main house.

Workshop will need:

windows

another wall

doors

cooling and heating system

Bathroom etc...

I can build build more units attached to the current workshop since there's so much land to play with 

but i have no idea of the cost.

I purchased this home for $150k in 2016

I owe 143K

last month I paid for an appraisal and the current value is at $185

(flooring was the only improvement at the house).

Question is should I refinance and bring in sewer line, build more units or live it the way it is?

I feel that there's so much need for rentals that I can really take advantage of what this house has to offer.