A ton of wholesalers and flippers, but not a lot of developers.  1) I've never tried getting financing to buy the land, I typically buy my land cash so I'm not incurring holing cost while waiting for approval 2) it should not be difficult to get a construction loan, I know lending one offers new construction loan, for my deals I've got a private  lender that borrows me money 3) The way I structure my deals, I'm paying out of pocket for all soft cost engineering, architect,  soil test, impact fees, I left out 2 critical steps on my initial write up Soil test: I'm ordering a soil test as soon I put the lot under contract, the cost is about $500, the county would want to see the result of the test when submitting your stormwater management plan Impact fee: Make sure to check with your county, some counties have them and some don't impact fees could be huge, in my county depend on where you build impact fees could be as much as $25k or $12k 4) I try to get as much as I can get done while under contract, In my county the typical turn around time is about 4months, while in Baltimore county I know builders that will close today and break ground the very next day, they have a faster permit process 

If youre going to change the footprint of the house typically you'll need an architect to get the plans approved with the city, the fire inspector will probably ask for a rendering of what the sprinkler system will look like, there are towns that will allow you to do a simple lock p and others that will ask for something far more complex.

My question is If I pay to have a lawyer work with me and pay the engineer/ architect to draw the plans needed couldn’t the seller turn around and list the property once they memorialize that new approved use.

If you start with an architect to design the guest house you might have $20,000 to $40,0000 wrapped up in engineering fees.

Architect?

I estimate total cost of the project at $200k, so this architect would represent 15% of total cost.

@Emanuel Escarpita after confirming zoning, you need to work with an architect to see what the FAR restrictions for the lot will be.

Sounds like your friend needs an Architect.

I'd strongly suggest looking for an architect that works hand in hand with a builder, or look for a design/build firm.

The listing agent seems to think that it’s no big deal, they just press a button and change it once you ask but I know after my phone calls to the zoning board that I need to hire a lawyer and an engineer hopefully not an architect as well to prepare the plans/ blueprints and anything else they require.