I have made the base for the first part of the railroad. I made the frame from 3" x 3/4" planed pine with 1/4" (6mm) MDF top. I don't normally use MDF - my usual base is Sundeala board but this only comes in 8' x 4' boards at nearly £50. I used it because it was designed to take pins and holds really well. However, I found myself hot gluing the track down on the last railroad and that seemed to work well with N Scale so I could economise and buy 2 x 4' x 2' MDF boards at about 1/4 of the cost!
Each of the boards has some M6 T-Nuts underneath with 35mm bolts inserted. These are used to level the boards as I am placing it on a table - given that we are only renting and we have to move again in about 8 months time.
I have posted the layout for the main board track. The subsidiary board is a 'fiddle yard' where I can build up trains to send onto the main board or receive trains. Part of one of the lines on the 'sub' board will be isolated and controlled by a DPDT (double pole double throw) switch so that it can be powered from the DCC Controller main feed or by the programming track output.
This is what it looks like at the moment. The fixture to hold the two boards together is yet to be done. There are two dowels between the boards that ensure alignment.
I have all the points from the previous layout and a box of 25 yard lengths of flexi-track arrives today so I should be laying track soon!
Just for the record - when we move to the next apartment - next May/June time, it should be the final move for a few years so the grey table you can see will be the base for the main layout and what I am building now will be the subsidiary board. At that time, the connection here to the 'fiddle yard' will be the connection to the main board.