Learn English – correct form of this sentence

I think the key to understanding this sentence is knowing that “burn building” is a special term (like “cash machine” or “slaughterhouse”). From what I can gather, the term refers to any building used for training firefighters by simulating the conditions of a structure fire.

Traditional burn buildings, built with special materials, can withstand multiple fires, although they do break down over time. Traditional burn buildings exist in communities, at fire academies and on university campuses. The fuel used to ignite fires in these structures is typically straw, hay or wood pallets.
_{Source: howstuffworks.com article: How Firefighter Training Works, §3: Burn Buildings and Firefighter Ranks}

With that in mind, this bullet point informs us that two things are being built on the training site: a house structure (presumably to train firefighters on moving through a house and checking each room according to their training) and a burn building, in which firefighter trainees will have to contend with the presence of an actual fire as they move through the structure. Here’s a picture of one such structure in use:

In your example, the due date is already Monday, so you are asking for an extension of time on the due date.

extend the due date to Monday

is incorrect in your example, since the due date is already Monday.

end of the day Monday

may mean the end of business-day Monday, which is not what you want.

end of Monday

is closer to what you mean. However, to avoid ambiguity, teachers will usually specify

due by midnight on Monday

So you would be asking for an extension until 1 minute before midnight, which is essentially midnight. In the current age of electronic assignment submissions, it can be easily enforced.

If your teacher only specified "Monday", you would have a valid argument that midnight is still a valid time to submit your assignment.