Tax laws for selling and reinvesting in real estate.

I need some advise regarding the tax laws for selling rental property and reinvesting into another property. The catch is that I plan to sell the rental property and build a spec house myself with the money. I know that if I were to buy another rent house, I would have around 120 days to close on it to avoid paying capital gains taxes. However if I build a spec house to sell, how would that be calculated? Would it be based on the "completion" date, the "sale" date, or what?

Also, I have another rent house with 2 other owners (1/3 ownership each). If we sell this house, can I reinvest MY 1/3 capital gains into other real estate with out paying taxes on my 1/3 even if they don't reinvest their portions?

Thanks for the help.