The increasing generation of agricultural, wood-processing and plastic wastes has created environmental challenges while also providing opportunities for developing alternative construction materials. This study experimentally and analytically assessed the structural response of particleboards produced from rice husk, sawdust, ground oil-palm fruit fibre, breadfruit seed coating and shredded plastic. Medium-density fibreboard (MDF) was used as the control. Scaled roof-beam models were investigated using experimentally determined modulus of elasticity and a similitude-based analytical procedure derived from Murphy's engineering similitude framework. The model length was 200 mm and the corresponding prototype length was 3600 mm; the prototype width and depth adopted in the analysis were 225 mm and 300 mm, respectively. The measured modulus of elasticity ranged from 0.35 to 5.90 N/mm². The adopted scaling procedure gave predicted prototype loads ranging from 37.21 kN for shreddedplastic particleboard to 193.50 kN for rice-husk particleboard, while the MDF control gave 205.64 kN. Prototype deflection predictions were very large, particularly for the low-stiffness plastic board. The results indicate that the investigated boards, in their present form and under the assumed beam configuration, should not be regarded as qualified primary load-bearing roof members without further optimization and full-scale validation. Among the waste-derived materials, rice-husk and sawdust boards showed the most favourable overall response. The study demonstrates the usefulness of similitude-based modelling as a preliminary assessment tool while emphasizing the importance of dimensional verification and full-scale structural testing.