The integration of artificial intelligence within the construction sector is effecting a paradigm shift in design and planning methodologies. In the realm of recent innovations, large language models (LLMs) have garnered significant attention. The effective integration of LLM with building design remains challenging, particularly in contexts that require adaptation to stringent local regulations. The objective of this study is to analyse the potential of LLM to support building design and construction planning. The study explores the impact of general-purpose LLM on process automation, resource optimisation, and regulatory compliance. The methodological approach adopted in this study is centered on a basic building design in Ecuador. The designed case study will be tested through specific prompts into LLM tools to validate its compliance with local construction regulations. Furthermore, LLM tools are tested in order to generate a preliminary time and cost plan. A comparison of experiment results with real data is undertaken for the purpose of evaluating the efficacy of the predictions made by LLM. The findings of the experiment demonstrate that LLM tools exhibit superior performance in the domain of regulatory compliance certification design in comparison to their efficacy in cost and time planning. Nonetheless, it is imperative that a more extensive array of tests be conducted to ascertain the reliability of LLM tools. In any event, the accelerated development of general-purpose LLM has the potential to enhance efficiency and address the existing unreliability.