One of the most important aspects of the building stage in a skills based approach is to assess how well you are learning or building an expertise with the skills in your skill set. As you execute the actions from your skill set plan (from the planning stage), you assess your capabilities of learning the skills and make decisions based on your assessments. Depending on the type of action you are using to learn a skill, making an assessment can be easy. For example, if you are taking a course, your assessment is simply the grade you got on a paper or the course itself. Otherwise, you may have to self-reflect and make an assessment yourself; for example, you will have to make a self-assessment if you learn web development from a book. The decisions you will have to make include: dropping the skill from your skill set; figuring out other ways to learn the skill; and identifying ways to advance your expertise with the skill.
I recommend keeping a weekly diary as you build your skill set. In the diary, keep track of your progress with learning the skills (if you have reached measurable goals), provide context on how you are applying the skills, and highlight any milestones; all of which you can refer to later when you present your skill set with a professional website. In addition, you should record all of your assessments.
Self-assessments are difficult because they require you to evaluate yourself objectively. It is easy to be too critical or embellish how well you performed a given task. This is why you should have measurable goals to anchor the assessment.
Formal employment evaluations are a common way employers gauge your performance while working for them; they can be conducted on a quarterly, bi-annual, or annual basis. You should have a meeting with your supervisors to discuss the results (if it is already not part of the process), and make sure your discussion is centered on how well you are learning your skill set. If your employer does not have a formal employment evaluation, suggest having an informal employment evaluation where you meet with your immediate supervisor to get as much feedback as possible; likewise provide your skill set as the focus of your discussion.
Grade for a course or project can be used to evaluate how well you are learning skills if you are a student. If you have any questions about a grade, you should meet with your professor to discuss what you do not understand; ask for their suggestions regarding further development of your skills, so they can guide you to other resources. Professors usually tap into the latest developments in skills and subjects related to their field.
Take an online certification test or assessment. This is beneficial if you do not have another way to assess your learning of a skill, for example, if you read a book.
Peer Reviews are effective if you worked with a team to develop a skill (and some skills are exclusively team oriented, such as project management).
To summarize, assessing your progress in learning skills is very important part of building your skill set. You will continually make decisions on how to proceed with the development of your skill set based on your assessments.