The design of your layout will be governed by the space you have & naturally your budget. Some like to base the design on a real life exciting or old track that used to be. Some will base it around a goods yard or large station layout. I, like many others have made my design so suit my garden allowing for some expansion at a later date if wanted.
The base & Type of layout:
There are a few ideas on what to build the track on & at what level suits you. Some will remove the turf/grass to have a channel that can be lined with a garden weed barrier cloth that can be backfilled with a gavel to lay their track on. With this you can lay flexible conduit under the gavel for electrics if needed. Others will put in a foundation & build a block/brick wall to run the track on. You can also build some flower beds & run your track through a scene like a jungle or desert. Some of these might depend on the climate of where you live. For myself & my age i am going down the route of building a raised track to save being on my hands & knees & getting backache once built. So i have aimed at 24"/600mm high & because i have the room, around 3'/1met + in from any boarder to ease cutting of hedges.
Control of everything
I decided to go down the route of RC "radio control" trains that have onboard battery to power them & 12 volt to power for signals, lighting & points. The points will have a 12 to 5 voltage reduction as the servos i am using run on 5 volt. This will all be controlled via ewelink home automation system that is simple to use & very cost effective. "£8.00 a year" & a 4 switch relay at £6-£10. This will all run off of wifi via my laptop, phone or even Alexa. I have extended the wi-fi range with some TP Link Deco M4 at around £100 for three & now have great wi-fi in every corner of the garden & also garage.
My Track Design
To raise my track off the ground i looked at wood, bricks & blocks & composite materials. "Plastic wood" & had a bit of a eureka moment with 48mm scaffold & fittings. This i am finding to be very adjustable & strong.
What i have done is bored a hole every 1met to set the scaffold upright pole in Postcreate. But just before i started, decided it would be an idea to Postcreate a sleeve in the ground for the pole. This was done using 50mm waste pipe so the 48,3mm scaffold tube can be easily removed at any time but still be solid. I did this by sliding a 60cm length of waste pipe over the scaffold tube & gaffer taping it. From this point a simple vertical tube & waste pipe around 24"/600mm in the ground & 24"/600mm sticking out the ground & then a horizontal tube at around 350mm/14" long so i can sit the track base on, which is 2 X 150mm/6" composite decking boards. So we got a rustproof tube & a base that needs no maintenance. The tube will end up like a crucifix in shape, with the decking boards on top either side of the T. Now the second-hand scaffold of 500' with lots of fittings & boards as a job lot was £600.00. The decking at 135met was £650.00 delivered + the sleeves & procreate at £350.00 Total £1600.00 for what is 70m/ 230ft X 2 base for the layout is not to bad. Layout link