44AD OR 44ADA for Architect

Sale & purchase under the same banner of proprietor ship firm?

Or any different firm for such business activity?

Though he can declare the sale consideration along with his professional receipts, but it will be expensive event.

If you are billing seperately for goods and services, you can show trading of goods under 44AD and architecture fees under section 44ADA. 

You have to show the professional Fees of 2 lakhs as income in ITR. In gst you have to show that income in Annual Return and pay the gst via DRC-03