Utilities your greenhouse will need:
Water: for plant needs; install an ample number of hose bibbs, strategically located for convenience. A tub is useful for washing pots and general clean-up use; supply it with hot water if possible, and install a mixing faucet with hose thread, so you can water plants with tepid water.
Electricity: for operation of basic optional accessory equipment, and for illumination (strip fluorescent lights at the ridge are practical). Provide an ample number of grounded outlets for operation of immediate and future accessories, cooler, humidifier, soil heating cable, etc.
Caution: The walks of the greenhouse are usually damp or wet; soil in the benches is wet and a hose can be carelessly used. It is therefore extremely important that every piece of electrical equipment in the greenhouse be grounded in an approved manner.
Gas, oil, or electricity (for heating)
For a free-standing greenhouse, be sure to provide for these utilities before the foundation is poured. All utility lines can usually be laid in the same trench.
A plain dirt floor is best, covered with gravel or crushed rock. It won't dehumidify the air and dry out your plants. Aisles of slate, brick or building blocks are attractive - or concrete aisles can be poured, wide enough to support the front bench legs with bricks under the rear bench legs.
A concrete slab floor isn't necessary - it won't provide the natural drainage of an earth floor, so pipe drains to outside or a catch basin must be provided. Also, a complete concrete floor makes extra watering of your plants and flowers necessary.
If your greenhouse is to be built other than "on-grade" - say on the roof of a building - a waterproof floor is necessary.
If your greenhouse is to be used as a solarium or conservatory, certain precautions must be observed during installation.