Shoot for the lowest down payment and ask what influences their proposed rate & down payment amount.Often the down payment will be 10-20%.If your down payment is applied directly to purchase price:Your down payment + principle balance = 200k purchase price50k (construction budget) held backAs @Kerry Boyle said, there are some lenders that don't have you pay interest on "undrawn funds".

Also having a hard time understanding how to value cost of build vs value of this future property so as to know what type of return on investment to lender I can offer without shooting myself in the foot or causing myself a hard situation unknowingly and not gaining as much equity as expected from building a second Building on the property.

Going to shoot you a PM!

Could you shoot me details on that?

It sounds like you're somewhat shooting in the dark with your offer.

Would love to connect soon, just shoot me a message. 

I would shoot for at least triple digit returns on your money unless you have a lot of it or you will run out quickly.As an example, if you can buy a used mobile home for $7500, you could rent it for $800 a month or lease option sell it for $15,000 with $3000 down and $650 a month payment.

Sorry if my post didn't make that clear but the goal is not to be hands off or identify if this was not actually for me.I'll shoot you a message offline, I'd love to chat more in depth about what you're doing!

After you do that, I would recommend having your agent walk it, shoot a video and send it to you. 

If you need anything shoot me a message.