Speech technology has matured so that voice-based reporting utilizing speech-to-text can be applied in various domains. Speech has two major benefits: it enables efficient reporting and speech input improves the quality of the reports since reporting can be done as a part of the workflow without delays between work and reporting. However, designing reporting voice user interfaces (VUIs) for professional use is challenging, as there are numerous aspects from technology to organization and language that need to be considered. Based on our experience in developing professional reporting VUIs with different stakeholders representing both commercial and public sector, we define a design space for voice-based reporting systems. The design space consists of 28 dimensions grouped into five categories: Language Processing, Structure of Reporting, Technical Limitations in the Work Domain, Interaction Related Aspects in the Work Domain, and Organization. We illustrate the design space by discussing four voice-based reporting systems, designed and implemented by us, and describing a design process that utilizes it. The design space enables designers to identify critical aspects of professional reporting VUIs and optimize those for their target domain. The design space can be used as a practical tool especially by designers with limited experience on speech technologies.