Sunspaces serve three main functions: they are a source of auxiliary heat, they provide space to grow plants and have fun living areas. The design considerations for these features are very different, and although it is possible to build a sunspace that will serve all three functions, some compromises will be necessary.
If the primary function of the room is only to provide heat, you can maximize heat gain by using sloped glazing, some plants, little thermal mass and insulation, unglazed end walls. Where winters are sunny in your area, carefully sized thermal mass will prevent extreme overheating during the day. In practice sunspaces rarely built to serve only as heating because there are cheaper ways to deliver solar.
If space will mainly be used as a greenhouse, remember that plants need fresh air, water, lots of light, and protection against extreme temperatures. Greenhouses consume energy through the growth processes of plants and evaporation of water: one pound evaporating water uses about 1000 kJ, which would otherwise be available as heat. Plants require overhead glazing, which complicates the construction and maintenance, and glazed end walls that are net importers heat losers. The bottom line is that a sunspace designed as an ideal garden plant environment is unlikely to have much energy left over for additional space.
Most people want to use their sunspaces as year round living areas, so sunspaces must have minimum glare and only moderate humidity. Carefully sized thermal mass will greatly improve comfort levels by stabilizing temperature extremes. Thermal mass materials should be placed in direct sunlight and should not be covered with carpets, furniture, or plants. Movable window insulation or advanced glitter at night to minimize heat loss and improve comfort.