For an accurate assessment of biodiversity trends, the only actual financially reasonable possibility to collect the necessary huge amount of standardized as well as opportunistic biodiversity observations data is by the involvement of large number of volunteer observers. The use of Spatial On-Line Analytical Processing (SOLAP) platforms allows non-experienced IT users to make easily geo-decision analysis and data exploration, which is not the case with the Volunteered Geographic Information (VGI) systems. Various overlapping VGI user categories are involved in this data collection process, each with its interests in biodiversity data, which makes problematic the design of a spatial data warehouse(SDW) model. Although various systems allow collaborative conceptual design for generic applications or for collaborative Geographical information systems(GIS), none of them supportsexisting DWs design methodologies; they do not consider together all decision-makers preferences. We define a new generic and participative SOLAP design methodology, which relies on a Group Decision Support System (GDSS) to support the collaboration of users engaged in the design of the SOLAP model. Intended to provide computational support to participative decision-making processes. The proposed methodology is participative since it allows groups of users to design their SOLAP models together and it is a generic methodology which is applicable in other contexts, such as environmental or health issues