That's all very well if you can spare the time. I'm sure many of us can spare no more than a month there unless you've already made the move for good.
Thats true but unless you have people here to send the money to that will spend it honestly where it should be spent then it might be worth taking off an extra two months from work. Its a tough one I know..

We built our place from scratch completely from the UK..We sent them rough plans of what we wanted with pictures sent by email..They had drawings done by the head municipal engineer who also issues the building permits required..They sent us a copy of the plans by DHL and we approved them.. The permits were issued and work started.
It takes a great leap of faith to send huge heaps of hard cash..
My brother in law tells me that it is common practice here for family members to divert large amounts to secret bank accounts and simply tell the sender that the project is over budget..
We are very fortunate and I could not in good conscience advice others to attempt the same...Just in case it all goes horribly wrong!!
No wonder a lot of people overseas come here for a month and buy ready finished houses in new sub divisions.

I've heard that many workers are quite slow so it could be quite a chore being on site for the duration.
Of course they are slow..They are on day work! The more days they work the more money they end up with. (Same in UK)

Can you get workers to agree to a price and duration like you can in the UK?
Of course!! The problem you now face is will the foundations have the tie beams they quoted you for? Will the posts and beams have the correct size rebar?...and so on.
You need someone that you can trust to be there to oversee just about everything.
I guess you need a reliable site agent to oversee works when you're not there.
Yes..Thats exactly what you need. Make sure you get one.