Recommendation is always the best way — ask your friends and neighbours.
The important consideration is quality and value for money.
You could save money on the erection, and then have months of chaos when the roof leaks every time it rains!

Ask what systems they use for windows, doors and roofs — these vary, not only in
quality but the ease with which they are erected, and their long-term performance.

The Aztec Conservatory Roof System, for example, has been designed by people in the industry for the industry, so is “fitter-friendly”, so is quicker to erect (so there is less disruption to you and your life) and more reliable with reduced risk of leakage.

Most importantly, check to see if the system has independent endorsement — BBA or BRE/Wimlas certification. This verifies the conservatory components, particularly the roof, will withstand climatic conditions such as severe wind or rain.