Development costs for small multifamily

[Caleb Webster]

I'm in the process of underwriting a potential development opportunity in SE before I make an offer. The plan would be to hold the property as a single family rental for a year or two while beganing the development process. For those of you with experience developing small apartments in the PDX metro, what are some of the 'back of the napkin' development calculations you make when doing cursory underwriting?