I've got my car in with the mechanic now and i say I'lll be loooking at a rebuild, so i was thinking while the motors out maybe i should just get the motor worked..
i was after some reccomendations as of what to do to the motor or should i just let the mechanic know what i want at the wheels and let him do what he thinks?

Let us know what you want at the wheels and we'll tell you what you need.

Head gasket

...or should i just let the mechanic know what i want at the wheels and let him do what he thinks?

 
I'd think that would be like giving him your bank account details and saying help yourself.
 
Unless he's familiar with 3sgte not the best plan, like RobK says, say your budget and intended use for the car. Daily, track, drag or hard parking?

I think if you are going to be increasing the power in the future but not sure what path your going to take and are rebuilding the engine now I would do the following as a minimum.
 
Forged pistons
Head studs
Metal head gasket
Maybe forged rods (Eagle rods are cheap these days)
 
Also maybe a decent clutch whilst the engine and box is apart. Soemthing that can handle say 250KW atw.
 
Then down the track when you slap a big turbo on you won't need to open up the motor again. You would have to take the valve cover off to install cams and gears though if required.
 
My 2c

lol yeah i suppose it would be.. anywhere from 300 to 350 kw at the wheels as a daily driver, possibly a bit of track a bit later on...
the bloke reckons ill be looking at 8k, worst case scenario for the rebuild of a 3rd gen 3sgte my budget depends on how long he can keep the car lol, but I'd like to draw the line at 12k

lol, anywhere from 300-350kw or hp? big difference. you need a gt3076 and significant engine/fuel/ecu upgrades for 300+kw. thats 400hp+

I spent about 25k+ for 316KW.
thats with me sourcing all the parts cheap frpm OS.
 
I reckon you'd be looking at about 30-35K if you were to ask a mechanic to do the lot for you.
 
the mod list for 300-350KW is long :)

maybe 350 is a bit much .....
It's got a new ceramic clutch in there atm just with those parts there skylighter, what do you think I'd be paying for that.. ball park

haha a list too long for my pocket atm.. maybe i just get the motor strong to handle the upgrades and build it in about 6 months

I think you need to find out exactly what 8k gets you from this guy.  300-350rwkw is alot of power.  You will need headwork to accomplish this in a sensible fashion.  I think a realistic budget to get the motor (inc head work) and clutch for this build would be $12k.  You'll see very little increase in power immediately though if you are only running the standard turbo, ecu etc.  I did a fairly comprehensive quote up for a bloke recently and for a car that will do 450-500whp you'll be looking at around $17.5-18k between an engine and bolt on components required to support the power.  This doesn't include labour to install the motor and all aftermarket parts nor includes tuning costs, only parts and machining and labour for engine assembly.
 
I can do you a motor for probably just under 10k that will do 350rwkw or more (I was building it for 500+RWKW, for 10k I could probably fit it, but aftermarket ECU would almost be a prerequisite = more $$$).  Realistically you could probably get a SAFE 350rwkw capable engine built for $8000-8500, plus installation costs.