Why use sources of information?
Though making your own plan may seem daunting, you can draw useful information from numerous sources that can help with preparing a plan of the chosen area. Having a plan allows you to consider carefully what you want to achieve. Likewise, consider the features you want to accommodate include: hard landscaping (e.g. patio, paths, pergolas, raised beds, fences and building), soft landscaping (e.g. lawns, trees, shrubs and herbaceous beds) and dedicated productive areas such as vegetable or cut flower beds. It is much easier to change the design on a piece of paper than in situ.
Alternatively, seek help from professional garden designer. However, even then you need to consider the criteria that the designer should fulfil (see seeking professional help below).