Land valuation

[Phips Deus]

A seller responded to one of my direct mail pieces and has an undeveloped 4 acre piece of land zoned for residential use in Marietta. Since I have never done a land deal, i am very inexperienced in doing comps for it. Is there anyone that might be able to point me in the direction of a resource where I can learn to do comps on land? Also Does anyone know developers that might want to build on a 4 acre piece of land in Marietta, GA?