construction heater wire requiarements
10 AWG wire.  

THWN type if in conduit. 

NM type if using plastic sheathed multiconductor cable.   10 AWG is typically orange.  10/3 if it needs neutral, otherwise 10/2 and re-mark the white wire as a "hot" by wrapping it with black tape.

Many 240V heaters do not need a neutral. But if you include neutral, you may thank yourself later, because it'll give you the most versatility in terms of other things you might plug in there in the future.   

You can also look at the plug for your heater and see what it requires.  Even if it doesn't require a neutral, you are perfectly welcome to run a neutral, and simply cap it off in the electrical box for future use.  

You must choose. You are not allowed to put 2 receptacles on a 30A supply cable in this type of installation.  The NEMA 10-30 is bad news and should be avoided, anything that requires it, you should replace it with 14-30.