Following are few travel tips so you are better prepared for the journey.
While there are few methods of transportation, the best method is to rent a car with the driver. If you are traveling with your family, a van would do. If you travel with a large crew, a luxury buses are available for rent. I'm sorry but I cannot recommend a cab service for you as I use my own vehicle, I have no experience using one. There are no train services available to Sigiriya. So you have a few choices and if you can spend the time, and bare the heat and dust, you could catch a bus.
You have to remember, that Sigiriya is in the dry zone of the country and it is very hot and dusty. Also, Sigiriya is situated off the main highway (refer the map). So, money spent on an air-conditioned cab would be a vise investment as it will allow you to be fresh and ready to explore upon reaching Sigiriya.
There is a rest house and many lodges near Sigiriya. These are not top of the range places but the few I visited were clean and served well. In my personal opinion, You will need at least one and a half days to cover most of the sites at Sigiriya. So, plan on staying a night there.
Try to travel light, when you climb the rock. The ascent is quite difficult if you carry a heavy load in your bag. A backpack would help you a lot, while a side bag would be a real pain to carry. Carry a bottle of water, you will be really thirsty by the time you climb to the top. Don't leave your empty water bottles on the top. Please bring them down and dispose them in the garbage bins available near the car park.
There are no toilets at the top of the rock.
Remember to pack a face mask for the trip. A scarf or a handkerchief could also be used to cover your face if you forget the face mask. Local convenient stores sell face masks for motor cyclists which provide excellent protection from dust and fumes. Sunglasses are a must to help you protect your eyes from dust and debris blown with the wind.
Climb the rock only if you are in good health. If you have fever or you are weak re-consider whether you can meet the physical challenge.
If you travel with small kids you might have to carry them on your shoulders. Mind the height, as there are pretty tricky places.
At times very high wind speeds are experienced at the top of the rock. Don't wear large baggy clothes which can act as a sail and throw you off balance. Wear cotton clothes and carry a small towel if you sweat a lot.
Wear sunscreen and lip balm to protect your skin from heat. A hat with a strap would help you a lot while an umbrella would be useless due to the narrow corridors and sudden high wind gushes.
Have a good trip!