The last decade has been characterized by times of change, including increasing levels of globalization and competition. Collaboration allowed SMEs to respond effectively to the development of new complex products and services but presented new barriers concerning the management of their business processes and relations with partners. This paper presents a new collaborative aggregate planning for non-hierarchical business networks, where SMEs collaborate in the selection of partners and definition of the operations plan required to specify, manufacture and distribute a custom made products. The proposed approach is based on negotiations undertaken by the partners in order to promote the creation of alternative operations plans and allow a multi-criteria evaluation of the involved costs and delivery dates. The proposed approach promotes the reduction of communication between partners, a reactive analysis of changes to planning and associated impact, enhancement of trust (since all partners have the same weight on the decision process).