Formal and literary. You'll see it on plaques, inscriptions, and in historical writing — but never in casual speech. Everyday equivalents are 创建 (chuàngjiàn) or 建立 (jiànlì).
memory
肇 carries the meaning 'to begin / to initiate' (as in 肇始 'origin'). 肇建 is therefore 'the originating-build' — the very first founding.
