Coverglass reduce evaporation and heat loss so your heater doesn't have to work as much. Get glass that is 4, 5 or 6mm thick rather than the 2 or 3mm thick coverglass sold in pet shops. the thicker glass is more expensive but less likely to chip.
If you don't want coverglass, you can make covers out of Perspex (clear acrylic).
Wood surrounds/ hoods can be made to any size or shape and can be made at home with a hammer and nails, or you can get a professional to make you something if you have money spare.