Just a few questions:
* Only orchids, or also bromeliad's, begonia's, water plants, epiphytic cacti, ferns, mosses or anything that likes a humid and semi-shaded environment?
* How high could the structure be? You prefer square/rectangle/round/free shape? Would it have a water sprinkler/misting installation?
* Will the structure be in the open field or close to a house or big trees? Will it have enough 'air flow' or does it need extra ventilation? What about electricity?
* Does the orchid house need to have a place to sit/relax with many people and/or a place to work with the plants, and possibly store potting materials?
* Do you need a 'separate' area for the 'youngsters/cuttings', or the ones with a different water-regime?
* Do you prefer to have your plants in baskets and pots, so you'll be able to move them when they get bigger, or flower, or need to be photographed? Or you want them 'fixed' to poles, roofs and riggers, buried in media in the soil as well?
* Are you the type that likes the 'jungle' look, where plants 'can do whatever they want', or the type that likes them 'organized', displaying their beauty at eye level and away from it's neighbors like in most nurseries?
* Any idea what sort of orchids you want to grow? The 'showy' colorful hybrids and/or the more 'hidden' wild Thai orchids?
* I understand 'non-rustic', so no fake cart wheels, (cement) tree trunks, garden gnomes and other kitsch, but how modern is modern? As in a 'plant gallery'?
I know... a lot of questions. But answers might help you to define a more specific brief. And us, to help