I don't have any experience of greenhouses in a tropical region. But here in Malaysia we have shade houses using 50 - 70% UV-resistant shade-cloth or lath houses using wooden slats to provide the required shade.However the latter is very expensive (timber being very costly nowadays). I myself have an orchid house measuring 12ft x 40ft, a combination of using shade cloth and wooden slats. I have installed an automatic overhead sprinkler/misting system; all of which keep my orchids quite happy. My orchid house is strictly DIY and cost about RM 2000 ( US $1 = RM 3.15 ).