When we land on a space that you own, you are allowed to buy houses and hotels.
But does the rule book say that you can only buy one house or one hotel per turn? Or can you buy more than one in the same turn?
You can buy more than one per turn.
According to the official Monopoly Millennium Edition rules, you can buy multiple houses per turn.
Following these rules, you may buy and erect at any time as many houses as your judgement and financial standing will allow.
Also, you don't have to be on the space that you want to make houses on to put houses on them.