Costs to consider are higher holding costs due to higher taxes initially. Then, assuming 18 titles already and approval by the municipality, costs before sales are:
a) seeding reserve fund or upgrading major items like roof, boiler, balconies, landscaping, hallway carpets, windows, parking lot, .... budget $100,000 to $300,000 depending on age and intended quality levels
b) interior in-suite upgrades .. budget $4,000 to $24,000 per unit depending on target audience, intended price and unit size
c) marketing and sales costs .. 4-8% of sales price
d) financing fees to get 18 mortgages or partially dischargeable mortgage, budget 1% higher interest rate plus appraisals and mortgage initiation fees, another $25,000 to $40,000 or so
e) higher holding costs during partial sales phase (that could take 1-3 years) due to condo fees and higher management fees
I've done a few conversions successfully .. and aborted a few due to these costs. High risk - high reward and very cash intensive venture ! It can make you rich if executed well, or bankrupt you if done poorly.