Madam,
As you said in eariler reply,
Your invoice value 600,000 that is you collecting 600,000 from your customer and you paying Electical subcontractor 300,000 and to labourers 250,000.
Inother words, You purchasing some goods and services from Electrical & Labourers and same is selling to your customer by adding your profit of 50,000.
So, as a supplier of goods or services you should collect not only 600,000 from your customer but also, GST on entire amount and remit the same to Govt.
So you should collect 708,000 (600,000+18% on 600,000) (rate of tax assumed as 18%), and pay 300,000 to electrical contractor, 250000 to labourers and 108,000 to govt, remaining 50,000 is your profit.
You no need to bother about whether electrical contractor or labourers are registered or not...
Even they are registered or unregistered its doesnot matter for your Profit, it won't impact.
If you have still doubt you can Ask
Thanks