Also if this property is on septic that also can throw a wrench into the ability to call a space "a bedroom" as septic systems are sized and permitted based on the bedrooms.

In a city like Philly, you will face many challenges - you need to learn the market and know the neighborhood and the block and make sure all of your numbers are within reason, you need very reliable contractors, you need a to understand the permit process, you need to be familiar with market expectations. 

@Phil SheltonYou would need a civil engineer to provide a drawing to get submitted to zoning and get a permit if it passes zoning is most common This also depends on the road - if it’s a state road forget it as it will take a year to get approved and cost a fortune - if it’s a local road process not as cumbersome but don’t expect this to happen quicklyIn some instances you may have to prepare sight distances etc to make sure it’s safe to add a curb cut

Insurance- coverage for new engineering, permitting, etc8.  

You also mentioned meters, do you have to separate meters, get approval from the city and pull permits?

got out of flipping to new construction in our market in columbus ohio. licensed general contractor. when interest rates got high single family existing went down by 30% new builds sold at a 6% increase that year which demonstrated the desire and premium that new construction commands. never looking back. total control, rinse and repeat. we can get permits in 28 days. we can buy land cash in 21 days. we can build in 120 days to 140 days and keep moving. super scalable and easy and no risk. we build the same 2-3 Floorplans 

The permits and architecture was done prior to start.).For most people the finances are the limitation to scale.  

Before you sign anything, definitley pin down the timeline for permitting and building.

Quote from @Sherry McQuage: Make sure to check the zoning to make sure mobile homes are permitted there; check for any hazardous waste designation for the area; will you need to have the parcels surveyed out in order to sell the size you intend? 

Tahoe isn't ideal right now as the local community is vehemently anti-Airbnb and the permitting system is challenging to navigate.