Here's how I did it:
3 interceptors
2 armed with Pegasus autocannons on ONE side(port) and rocket batteries on the starboard side with shields.
1 armed with Barbosa autocannons on ONE side, nothing on the other, shields.
Sail the Barbosa-armed one up to visual range with the Construct and have it aim its cannons broadside.
Meanwhile, move the other two near the bottom of the map at a comfortable Pegasus range with their autocannon sides facing the Construct.
When that little green dot on its head is visible, it's vulnerable. Autocannons will fire at will and the rocket batteries need to be manually targeted to bombard it from above. Use the shields liberally, as the Construct's beam weapon is a beast with infinite range. From there, it should work itself out.