Matsya Purana — The Rite and Glory of Meru-Dāna: The Tenfold ‘Gift of Meru’ and Mountain-Offe...
तीर्थेष्वायतने वापि गोष्ठे वा भवनाङ्गणे मण्डपं कारयेद्भक्त्या चतुरस्रमुदङ्मुखम् प्रागुदक्प्रवणं तद्वत् प्राङ्मुखं च विधानतः //
tīrtheṣvāyatane vāpi goṣṭhe vā bhavanāṅgaṇe maṇḍapaṃ kārayedbhaktyā caturasramudaṅmukham prāgudakpravaṇaṃ tadvat prāṅmukhaṃ ca vidhānataḥ //
At a tīrtha, in a sanctuary, within the precinct of a cattle-shed, or in a house courtyard, one should devoutly have a maṇḍapa constructed—square in plan and facing north. It should slope toward the east and toward water; likewise, according to rule, it may also be made to face east.
This verse is not about Pralaya; it is a Vastuvidya instruction describing where and how to construct a maṇḍapa, focusing on orientation and proper slope/drainage.
It frames pavilion-building as a regulated, devotional act: a householder (or patron-king) should commission properly oriented structures in homes, shrines, and community spaces, aligning ritual practice with prescribed architectural order.
It prescribes a square maṇḍapa, ideally north-facing, with an auspicious/practical slope toward the east and toward water (supporting drainage and ritual purity), and allows an east-facing option when done according to rule.