The paper discusses the design and construction of a temporary structure in a neglected urban space. Researchers consulted and worked with members of a youth club in a deprived area of an English city to try to enable spatial appropriation through participatory design. It was found that age- and class-based relationships greatly constrained participants’ sense of appropriation. Participants did, however, appropriate the co-design process in enthusiastic ways centred on the transgression of adult norms. The article concludes with reflections on how constraints on marginalised youth agency can inhibit participatory approaches.