How to gauge pricing for hard/soft costs, etc?

Going through deals trying to learn.This property I'm looking at is in NYC. So I have asking price for land, can find tax info, what cap rate comparable properties are going for (the 8 and 6 below are numbers I chose to illustrate the point, I'll have to dig deeper into comps and add in a 150-250 bps premium and go from there), but trying to fill out the rest. This is for my practice and is not a model given to me by anyone. I'm basing this info on asking prices for deals on the market today.

Say land is $10 million and you can build a 100k BSF residential building. I want to look at it from a developers perspective and say I want to build to a 8 cap and sell at a 6 cap. This is for my practice, but I have no clue what to gauge for hard/soft costs. Land was $100/SF, from resources I've seen hard costs 3x that ($300/SF) & soft costs were 1x ($100/SF) based on this asking price, but that's obviously market dependent. How do I find out these costs with no info given since this isn't a modeling test. It's literally me trying to build a quick test on if this passes and gives me enough profit to take the risk and if not what price will do that. Is there a general rule of thumb with these costs? I'm not in development this is all theoretical to get reps in.