When buying an under-construction flat, you'll typically encounter two agreements: a Sale Agreement for your Undivided Share of Land (UDS) and a Construction Agreement for the flat itself. This structure is common as you're purchasing a portion of the land and the builder is constructing the property on it. Be aware that the registration value is usually based on the Sale Agreement's land value, which can impact property valuation and bank approvals. Seek professional advice to navigate these complexities.