There is no one perfect method, but I will tell you how I would set it up.
Assuming it is for an adult...
A 3ft or 4ft vivarium depending on the size of the snake (I am inclined to stick to 3footers for royals though)
A ceramic heater at one end of the viv on a pulse proportional thermostat with a bulb guard
An accurate thermometer
A substrate of orchid bark (this is my person preference for any snake that likes humidity, people will tell you to use alsorts if things and in the end its up to you)
At least 2 hides (either special reptile ones or pieces of corkbark) placed at both the hot end and cool end of the viv
A decent sized waterbowl
Some plastic plants etc to decorate
It all depends on the size of the royal as to the size of the viv required.Royals tend to prefer a smaller space to large open vivs.If memory serves me right temps should be around 88-90 for the hot end and 78-80 for a cool end.They do not require uv lights so you can use heat mats and spot light lights for a basking area or ceramics and a low wattage bulb.
I've got a 3'x2'x2' wooden viv, with glass doors.
I use a 30 watt heat mat attached to 1 side of the viv, in winter the heat mat is on constantly and the temp is controlled by a dimmer thermostat on a red night light, this provides the extra heat required.
In the summer I don't use the lamp and use the thermostat on the heat mat.
The viv should have a temperature gradient of approx 82* f in the hot end to 78* f in the cool end. provide a basking spot of 86* f max.
Lower the temp at night to 76*f to 78*f.
Humidity should remain at approx 50% all year round.
Use dark, damp bark substrate, a hide box and maybe a log, as they do sometimes like to climb. I also use damp moss to provide humidity.
Provide a large water bowl, preferably large enough for the royal to lie in.