Talk to your agent and don't try to hide material facts about what you're planning to do. 

I'd need to go to about 250K with 10/15K in materials to get around 320K and that's pushing it.

Examples would be incorrect square footage, incorrect year built, incorrect style of home or materials.  

The costs of land  , engineering , site work , permits , labor , and building materials make this virtually impossible . then there are zoning issues and the rest of the politics that go along with this . 

As a seller, you HAVE TO and should declare anything that would materially affect the value of a property aka a fire.

I pay roughly $1/sq ft for material and installation.

The all-in price should be right around $12 - $15 / sq yd, which will include the carpet, padding, all misc materials and install.

As you know, material, labor, and supplies for roofing can change a lot within a matter of weeks / months. 

I will not start work without a deposit big enough to buy the materials for that phase.

Anyway...to the lady who wanted to find tax liens...there is a ton of free material on youtube that will walk you throught the process.