There are lots of style for greenhouse. It could be arc, Quonset, gabled, atrium, lean-to, oval, round, installed against house, free standing, portable, others.
Greenhouse has different features to choose from depending on what you want to have in it. Benches, shade cloth, misting system, heating, lighting, insulation, tables, automatic window openers, ceiling fan, line voltage thermostat, hi-low recording thermometer, exhaust fan w/ louvers, glass storm door, plumbing/ water, gutters, others. All these are taken into consideration in the estimates.