LOL! The moon is 2,000 miles across [400 miles less than the width of Australia]. Unless the aliens are the size of chimps constructing mines that are equivalent to their height, then yes; An every day telescope could see it.
If they are on the dark side of the moon, they would be living in constant -280° Fahrenheit conditions with little to no atmosphere, concluding that they don't breathe, have a mass exceeding that of a large vehicle and are accustomed to the weather conditions, leading to the stable conclusion that they have no need for water as their bodies obviously wouldn't function on it for it would have frozen -280° Fahrenheits ago if such substance was present in them. Either that or they have developed suits to wear enabling them to breathe and remain grounded and at a comfortable temperature, meaning that their buildings must also be of that environment, making them gratuitous amounts larger than the average building, making it all the more easier to spot using your every day telescope. The crafts that transported the original materials in order to begin construction, our astrologists and satellites would have seen it coming when and if it did, unless of course they came pre-space era and are now living in the 10km deep crater on the dark side, hence not being aware of the multiple attempts at moon landings etc.