The cellular structure of the classifying spaces of finite groups
  In this paper we complete the description of the $B\mathbb{Z} /p$-cellularization of the classifying spaces of all finite groups, for all primes $p$. The techniques are based in a careful analysis of the $p$-fusion structure of the groups involved -with special attention to their strongly closed subgroups- and Chach\'olski's description of the $A$-cellular approximation. 
Ram\'on J. Flores and Richard M. Foote