DEVELOPMENT AND VALIDATION OF A CONSTRUCTION COST INDEX-BASED PARAMETRIC COST ESTIMATING MODEL FOR BUILDING FINISHES IN RESIDENTIAL BUILDING PROJECTS: IMPLICATIONS FOR AFFORDABLE AND SUSTAINABLE HOUSING DEVELOPMENT IN SOUTH-WESTERN NIGERIA

The dataset used in this study comprises two complementary data sources collected to develop and validate a construction cost index-based parametric cost estimating model for building finishes in residential building projects in South-Western Nigeria. The first dataset consists of historical cost records obtained from Bills of Quantities and final accounts of 60 completed residential building projects executed between 2011 and 2025. For each project, information was compiled on the completion year, total construction cost, building finishes cost, and the corresponding Construction Cost Index (CCI). Historical costs were subsequently normalised to constant 2025 price levels using chain-linked construction cost indices derived from annual inflation rates.   The second dataset consists of responses from a structured questionnaire administered to 415 construction professionals, including quantity surveyors, architects, builders, and engineers with practical experience in residential building projects. The questionnaire captured respondents' assessments of the relative importance of twenty-nine building finishes components grouped into seven classifications: wall finishes, floor finishes, ceiling finishes, door and window finishes, roof/external finishes, sanitary and fitting finishes, and external/compound finishes. Each component was evaluated using a five-point Likert scale ranging from 1 (Not Important) to 5 (Extremely Important).   The processed dataset contains cleaned and validated observations with standardized variable names, derived variables, and complete metadata. Derived variables include inflation-adjusted total construction costs, inflation-adjusted building finishes costs, Construction Cost Indices, percentage contribution of building finishes to total construction cost, Relative Importance Index (RII) values, and component rankings. No personally identifiable information is contained in the dataset, and all questionnaire responses were anonymised prior to analysis.   The dataset was analysed using Microsoft Excel and IBM SPSS Statistics. Descriptive statistics, Relative Importance Index (RII), Pearson Product-Moment Correlation, simple linear regression, and Analysis of Variance (ANOVA) were employed to examine the relationship between building finishes cost and total construction cost and to develop the predictive cost estimating model. The accompanying dataset, data dictionary, codebook, and README file have been prepared to facilitate transparency, reproducibility, and future reuse in accordance with FAIR data principles.