Hello - Welcome to CC and the Foundry
You should find some useful information in the [Official] Conquer Club Mapmaker Handbook
If you still have questions after browsing those topics, feel free to ask any specific questions in the Foundry Discussions subforum - you should find people eager to help and give any advice in there.
Unfortunately a London Underground can't be made due to copyright. Everything that says London Underground, connections, Tube is under copyright. Sorry to be the bearer of bad news, but it just can't be done
Here are couple of other attempts at it:viewtopic.php?p=3081078#p3081078viewtopic.php?p=2224417#p2224417
There are more, so suggest using the advanced search
to read up on all problems others had in getting a much needed London Underground map!
Good luck, hope you can get this done. If not, we hope you will come up with another idea!