Clear and well-written resumes can help jobseekers find better and better-suited jobs. However, many people struggle with writing their resumes, especially if they just entered the job market. Although many tools have been created to help write resumes, an analysis we conducted showed us that these tools focus mainly on layout and only give very limited content-related support. This paper presents a co-creative resume building tool that provides tailored advice to jobseekers. It is based on a comprehensive computational analysis of 444k resumes and the development of a Dutch language model, ResumeRobBERT, to provide contextual suggestions. Through the analysis of the resumes, we found that some expected sections, such as language proficiency, are often missing entirely, while conversely some resumes contain unexpected content, such as negative personality traits. This implies that jobseekers could benefit from more guidance when writing resumes. We aim to support them in the resume-writing process through our tool ResumeTailor, a co-creative resume building tool that gives textual suggestions and provides a template for important resume sections.