While dreaming is typically considered an unconscious process, and creating something consciously (may be 'sankalpa') is a distinctly separate activity.
Mahabharata, for instance, outlines the cyclical process of creation and dissolution:
With the commencement of Brahman's day the universe begins to start into life. During the period of universal dissolution the Creator sleeps, having recourse to yoga-meditation. When the period of slumber expires, He awakes. That then which is Brahman's day extends for a thousand such yugas. His nights also extends for a thousand similar yugas. They who know this are said to know the day and the night. On the expiry of His night, Brahman, waking up, modifies the indestructible chit by causing it to be overlaid with Avidya. He then causes Consciousness to spring up, whence proceeds Mind which is identical with the Manifest.
The above passage clearly mentions that universe is present in Brahma's day time only and it ceases to exists in his night time when Brahma is in Yoga nidra. There is no possibility of Brahma to be in dreaming state so that Brahma creates universe unconsciously in dream. But in general,people use to believe that universe is in dream of Brahma.
According to the text, the universe exists during Brahma's "day" and dissolves when Brahma enters a state of Yoga Nidra at "night". This process doesn't suggest that the universe is an unconscious dream of Brahma's.
So, my question is this: in which 'avastha' (state of consciousness) is Brahma in when he creates the universe? And why is the common belief that the universe exists within Brahma's dream, even though scriptures suggest it is a conscious creation?