How long is a piece of string??

I don't like being kept in the dark or things being out of my control.  Then why would you decide to build, I hear you ask.  And right now thats a very valid question.  We have a 10% stake in a road-less block of very flat land, a 5% stake in a very posh potential new home which leaves 85% of uncertainty.  We have a house to sell.  The market appears to be slowing.  Rentals are tight.  Our land is completely stagnent and there are 4 stages before us yet to title.  So when do we put our current home on the market?  Now and rent for however long it takes to have land and then house completed?  The land could be another 6 months away - maybe more.  The build is scheduled for 30 weeks from site start, but who knows when that will be, and by missing our October site start booking (which I'm sure we will - at a penalty of 2.5K per quarter) will we be pushed further down the queue?

Too many uncertainties!