It comes kind of flat pack - and is very easy to put together - slots together like a jigsaw kind of
Then the roof just lifts on and off. I would have a bendy bridge handy to put over the door though as the door is quite large and the bendy bridge makes it darker inside and adds a tunnel entrance
Not sure what nesting material you have, but torn up strips of plain white toilet paper is best really. Just take a few sheets and tear them into five or six strips lengthways and put a big pile of it somewhere in the cage. Don't put it inside the house - they like to take the nesting material, pouch it and take it to where they want to build the nest - you should see the pile go down gradually - sorry if you already know that!