For example, if your mental picture is one of a cottage garden bed with a brick path and riots of hollyhocks, backed by a picket fence and framed by a pair of rustic chairs, those will be the items you need to find first. Often, with a little thought, you can adapt or improvise with at least some of the plants and materials already on hand or inexpensively available. This is not to say to cut corners, but to evaluate each element in a fairly harsh light. Consider the brick path. In fact, a little informal brick path is well within the capabilities of most people, but it is time consuming and can be very hard work if done all at once.
Bricks are expensive, but there are ways to get around that.
The picket fence is somewhat similar. While you may be able to make a picket fence, there are nice enough yet inexpensive prefab fence sections available. Installing the fence is not a difficult job, but it does take two people. Digging the post holes is hard work. You can certainly paint or stain it yourself, or hire someone to do it all at great expense.