To be safe when picking comps, you want to identify several houses that are a very similar product to what you will be building and average them.
By falling in love with comparative sales, you are opening yourself up to the risk that there were other mitigating factors to cause the sale to occur at that price.
I am sure you have heard the mantra: Location, location location. It is true, location impacts the value of real estate tremendously. Real estate is hyper local.
If you cannot find houses that are very similar products to what you are building, you can start to make adjustments to the price. The more you adjust the value the more subjective it gets. This is why it is dangerous adjusting the values by too large of a factor from the comps you have found.