Is it a standard engine? Has it been run in yet? what oil are you using? when was the oil last changed?

Try taking off your intercooler to throttle body boost pipe, and check for oil in the throttle body housing, push throttle lever to check behind flap.
If oil in there then it could possibley your turbo.

Say you left it overnight and then started it in morning, do you get a puff of blue smoke straight away and then it clears? thats normally a sign of valves stem seals. Were these not changed in the rebuild?

When mine smoked it was a comination of the turbo and my bores had glazed.
It didnt smoke on full boost but on the over-run and then stopping at traffic lights, i would leave a smog trail behind me then it would clear.