Whoa! This is the first post in a long time by someone with more than 5 posts, that has votes (indicating they contribute)!!! Wow. I thought only new users and takers came to this forum...
Anyways:
Pre build, you can get an appraisal and will (likely) have to get one if it's being financed. What it appraises for and what it costs to build are independent of each other. You could get the appraisal and compare it to the cost to build and see how you feel about proceeding.
There's pitfalls in building in c areas and below. Theft, values, depressed rents, decreased ability to find a great tenant for your great new home, etc. What is the land worth? If the lot cost is minimal, it, to me, is a good indication that it is probably not a good area to build on. For instance, I bought a lot in a C neighborhood for $500. Building on it would have been extremely unwise for an endless list of reasons.
Now is a very tough time to build. Your best bet is to find plans and take them to several builders and have them price it out as completed. Beware tho - pricing will have a very short shelf life. Get a budget from them and see if you think it's in line. Anything not specifically noted will be done to the minimums. For instance, flooring, if not specified will likely be rock bottom carpet or laminate. Make sure you include specs for things you must have (like lvp or even, in some cases tile). Last, when they're building, make sure they aren't blowing through their budget, potentially setting you up to be out of funds with a home that is not complete. This happens sometimes.
To see if it's worth it: figure rents, taxes, insurance (get it priced - often new construction units are cheap to insure), cost of capital and see where you're at. New construction homes and units have a lot of upside.