Hi "Flipping"
Welcome to the forum!
I built my own home here in Coronado with a "Maestro de Obras" If you (or someone you really really trust ) speak Spanish it is feasible for you to do this too. It would also be recommended that you have experience in construction. Without both of these factors I wouldn't suggest it. If you have only one of these two, you can still try - but gird your armor for battle!
You will need an architect or engineer in any case because you must get approval from the city government for building. They may or may not ever come to inspect, but you need the permit to avoid complications during construction and in the future.
Definitely you have to look at properties they have built (both your contractor and the architect) and speak with the owners about their experience. For example I would recommend my maestro de obras without hesitation, but not the architect I used. Here are some other suggestions:
Don't Include Materials in the Contract Never, ever, EVER contract any person for any project with the materials included. It will never work! The second there is any type of delay (which there ALWAYS is), they will try to skimp on some material in order to make back their profit margin. And they will most likely end up asking for more in the end, because they miscalculated on the estimate or it will take longer than they thought. Another possibility is that they spend the money you gave them for materials on something else (women, liquor and/or gambling) and they leave the job half finished. Or the materials are purchased, but they never arrive at your construction site!
Don't pay by the hourYou should be prepared to pay your contractor a fair price with a fair profit for him. But don't pay him by the hour! You will get frustrated with the progress and feel like you are paying too much, even when you are not. And obviously there is a great incentive to slow down the progress, especially in the later stages. You will have a clear idea of how long your construction will take when you begin, especially once you have some estimates.
Always Buy the Materials Personally – and check the delivery!Feel free to get a list of materials you will need from your contractor and visit various places for estimates. You can almost always get 10% off by paying cash (as opposed to a debit or credit card) on anything other than the very basic materials, which are price controlled. You can also obtain a discount because you will buy in quantity. If you are building an entire residence, the construction depot or hardware store can give you a much better price if you will commit to them for the entire process.
Don't forget the freightIf you have your own truck or pickup, you can save a lot of money on freight charges. Otherwise, a depot that is closer may have a lower overall cost when you consider the freight charges from a place that charges less but is further away. On a related topic, try to check with your contractor around lunchtime for the materials he may need the next day. It is very difficult to get deliveries first thing in the morning, since that's when most people ask for materials. The best way is to call in the afternoon and have the order delivered before your crew goes home for the day.
If you are going to have a smaller home only on one story you might consider ordering a "pre-fabricated" or "pre-packaged" home. There are several companies that offer this and advertise regularly in La Nación. Some are with "super" block, which is like 4 cinder blocks stuck together. Or some are "baldosa", which are prefabricated concrete panels. I have seen homes from 42 m2 to 100 m2. The advantage is that they have great prices, pre-approved floor plans, all of the materials are included and free delivery to most areas. You save on the engineer's fees and I think they even get permits from the city for you.
The disadvantage would be that you would probably be unable to alter the floor plan in any significant way and that you would need good security on the construction site for the materials since I believe they all arrive at once.
Good luck with your adventure and please don't hestitate to ask any other questions.