Nowadays, complex software systems tend to be the result of operationally independent, constituent systems working together, arising a new class of software systems called Systems of Systems (SoS). In another perspective, software architectures are essential to promote the success and quality of software systems, even more on SoS. However, the construction of SoS software architectures is typically ad-hoc without well-defined and standardized architecting approaches. In this context, the main contribution of this paper is the proposal of a "Meta-process for SoS Software Architectures" (SOAR), which supports the authoring of processes to construct SoS software architectures. SOAR is also independent of application domains and it is based on a broad, deep literature review as well as knowledge of experts. In order to evaluate the feasibility of SOAR, we conducted a survey with experts in SoS software architecture. The results of this survey indicate a good acceptance of SOAR among experts that also provided insights for improving SOAR. Our intention is to use SOAR as a framework to support the authoring of architecting processes for SoS and, further, to provide specialized versions including architectural decisions for specific application domains. Therefore, in some extent, we hope to contribute to the development projects of the new, important class of SoS software systems.