To support new applications and services, networks must take into account Quality of Service requirements. However, QoS support increases the network complexity. Network development techniques must apprehend this complexity not only from a functional point of view but also from QoS point of view. Integrating QoS aspects early in the development process allows improving network quality. The object paradigm and UML in particular can help reducing QoS-aware network design complexity. To guarantee end-to-end QoS, Service Level Agreements must be negotiated between providers and users.. In this paper, we propose means for automating negotiation process at the design step. We also propose to integrate this negotiation in a UML QoS oriented approach for network design by exposing means to specify SLA.