Estimating fourplex construction costs

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I'm checking out the viability of tearing down a dilapidated SFR on a lot zoned R1 in SE Portland (Oregon) and am wondering how to estimate the costs of 1.) the demolition, and 1.) the construction of a new fourplex.

I'm aware of system development charges and have found documentation online to tally up those costs (including permits), but I'm not sure how to estimate construction materials and labor. Is the best way just to get estimates from local contractors (and can I even get a reasonable estimate without floorplans?), or is there a back-of-the-napkin way to get a rough idea to see if this approach is even viable?