There are different types of roof gardens, also known as green roofs, which vary in design, purpose and vegetation. Here are some of the most common types of roof gardens:

1. **Intensive Roof Garden:** This type of roof garden has a deeper substrate layer (usually over 6 inches) and can support a wide range of plants including shrubs, trees, herbs and even grass. Intensive roof gardens require more maintenance and irrigation than other types, but also offer more design options and aesthetic value.

2. **Semi-intensive roof garden:** This is a compromise between intensive and extensive roof gardens. The substrate layer is usually between 4 and 6 inches deep and can contain a variety of plants, but usually not trees. Semi-intensive roof gardens require less maintenance than intensive roof gardens and still offer some design freedom.

3. **Extensive Roof Garden:** Extensive roof gardens have a shallow substrate layer, usually less than 6 inches deep, and contain mainly sedum-like succulents, grasses and mosses. They require minimal maintenance and are lighter in weight than intensive and semi-intensive roof gardens. They are ideal for green roofs on commercial buildings.

4. **Biodiversity Roof Garden:** This type of roof garden is designed to promote biodiversity by creating a habitat for native plants and animals. It often includes elements such as beehives, bird feeders and small ponds to attract insects, birds and other animals.

5. **Vegetable Roof Garden:** Vegetable roof gardens are designed to grow vegetables, fruits, herbs and other edible plants. They are popular in urban areas where space is at a premium and can contribute to local food production.

6. **Rooftop Herb Garden:** This type of roof garden mainly focuses on growing herbs, such as basil, rosemary, mint and oregano. It is often small in size and can be used for culinary purposes.

7. **Medicinal Plant Roof Garden:** These roof gardens are for growing medicinal plants and herbs that can be used for natural remedies and medicinal purposes.

The type of roof garden that is most suitable depends on several factors, including the space available, the weight capacity of the roof, the climate, the intended purpose and the level of maintenance desired. It is important to select the right plants taking these factors into account to create a successful and sustainable roof garden.