Build costs with a 1031

[Julia Oh]

I am thinking of selling a property that has no mortgage for $200k. Approx $150k of this would be LTCG and recaptured depreciation. I am also looking to buy a property that is a tear down. Purchase price is $75k. My understanding is that the build of the new property needs to be completed within 180 days of the sale of the relinquished property. My question is whether the build needs to be complete complete or I just need to spend the remaining $125k before 180 days? I'm fairly certain it would be nigh impossible to finish the build in that time, given contractor schedules in my area but I know that I could definitely spend $125k as the total build cost will likely be more like $225-250k (plus the $75k purchase price).