We are re-building some perennial and shrub beds this fall. No garden is ever finished; most are usually in transformation. Having lost a large old Sugar Maple a few years ago, a shade border has become a full-sun border.
That's an opportunity, but it takes a lot of wheelbarrow and shovel work to prepare the beds (adding manure, peat moss, etc) and to get it planted before a frost - and I have a busy life. Designing a border is the fun part, and Mrs. BD has kindly told me that "It's your turn" to do it. Right now is the time to get the perennials in the ground, and shrubs and perennials planted or transplanted. Real gardeners try to plant in the fall, not in the Spring.
Most perennials can be bought online now for immediate delivery, while the local garden shop may have nothing but mums, asters, and pumpkins.
Part of the fun of design is ensuring early Spring through fall blooms, contrasting textures and heights, harmonious colors in the various bloom seasons, some degree of repetition, some plants which provide structure to the plan, something for winter interest, etc. It's a challenge, even if you are aiming for an informal "cottage garden." It's like painting.
Perhaps later I will list the plants I am putting in, but today just one of them: the late summer and fall-blooming Anemones (my pic from a NYBG border last week).