Will you need to use your solarium during the winter or are you looking for a 3 seasons’ room? In the first case, you would need a heated installation. The isolation would be superior to a regular solarium, the glass used would be high performing in energy efficiency standards (to provide more “natural” heating) and you’ll probably want to heat the floor with an electric system so your feet aren’t cold at all times. These could actually double the construction price of your solarium, so you might want to simply stay out of that room during winter!
Another possibility would be to forget about glass solariums and aim at verandas. They might be darker since the roof will be opaque, but the price of building this kind of verandas will definitely be lower.
Glass windows allow the sun to heat your solarium during winter… but during summer as well! During the afternoon, high temperatures could definitely become a troublesome issue if you do not plan ahead. If you plan to be using this room at that period, you’ll probably go for tinted glass. You might also want to install windows so that ventilation can be used as a weapon to fight overheating.
If you have a rather high budget, a few items can definitely enhance your solarium. A spa, for example, is indicated so that you can laugh at winter’s face (and at your neighbors!) at all times. However, if you decide to invest in a 4 seasons’ solarium AND a spa, you might want to work a few extra hours: the bill could rise pretty easily.
One thing you should also do would definitely be to work with a specialist. Professional advice on materials, ventilation and heating issues will help you to land the perfect solarium to enjoy summertime.