Well let me be the first to welcome you to the forum... The most obvious of first questions ever asked here...
Modeling is going to take you some time to learn this will not be an over night process...
Anim8tor is a good starting out program... Milkshape is also good but only has a 30 day trial...best to google it to locate those...
If you get to where your asking about how to build walls, add signs, make a door my best suggestion is look for Signs III and MagicFPS
Also just to let you know this forum is a wealth of information and there are a ton of models here so if you use the search feature below when looking for your model or read the stickies above there will be alot of detailed information you will be able to find usefull to you especially before asking... odd's are the question has been asked before...
Have you downloaded your CLiPs today.