If you really want to build the house, and plan on doing it in the next few years, then I'd forget about the apartment. If we get this "soft landing" that all the politicians and economists are talking about, your apartment will be worth about the same amount of money when you go to sell it in two/three years time. When you consider all the expenses associated with buying (legal fees, stamp duty perhaps, moving fees, apartment management fees, etc, etc), you may end up making a loss.
The econimists could be wrong, and prices may continue to rocket. But also prices may even drop. So consider all three scenarios when making your decision.
If you're sick of sharing, why not rent one of these apartments that you're currently considering buying. The way the current market is, your rent will probably be alot less than the repayments on a 25 yr mortgage on the same property, and you won't have to pay property management fees. In fact, the rent will probably be equal to the interest part of the mortgage, and interest is as much "dead money" as rent (unless prices continue to rise significantly above general inflation).