You can only do the suggested construction if you have full knowledge about it. It is easy to hire workers but if you do not know how to do it then the workers might just be doing their thing but not in the proper way. Think of the mixture of concrete, how much cement, how much sand, how much gravel, that couldn't be a guessing game. In other words, if you have no engineering knowledge then you cannot build your own structure. It would be foolhardy to be doing the construction just to make it cheaper for you. Also take note that there is a building permit required by the government which means you need an architectural plan for your structure, be it a house or an apartment. The plan includes the bill of materials to be used. Some people think that constructing a house is as easy as hiring carpenters and masons but it is a risky notion.