a contract or buidling a new house / written or verbal? and References?

In talking to building contractors, i've gotten a wiiiiiiiddddee variety of responses in how they bill and how they do their pricing. Some of you must have gone through this and have some lessons learned .....

One builder - no written contract, pay week to week, pay IMSS. Did give a start and ending date. One reference said he was good in meeting his schedule.

Another - charge is based on which 'level' you select ..... basic, standard or luxury. He can only give me a kinda/sorta response as to what is included in the basic, standard or luxury. I've asked for something in writing, but there is some resistence.

Another - $12,000mx per sq meter (actually that has come from 2 architects)

Another - cost plus 10%, and someone else was cost plus 15%.

What roughly goes into a contract?
I'm assuming an attorney writes this up?
Is it enforceable?
Or do you just make deductions in money to make sure the work is completed on time?

I've asked for 2 references from one guy with whom I have a tentative agreement to start. So far, i don't have them.
He was recommended to me by an architect who turned out to be someone I would not use. So that has cast a little shade on the recommendation.

Life here ... I appreciate your input!

Surely there must be someone on this board that has had a new house built and either had a formal contract or informal agreement and can comment on the parameters?

Just make sure you are there EVERYDAY...ALL DAY.....our contactor came in on time, on bid but because I had to split my time between the house and caring for my husband, corners were cut which we discovered after moving in.

thanks ....

We found out the hard way that even if you get an estimate, that really means nothing at all. The person giving the estimate may or may not know anything about actually estimating a job ... and in some cases he/she may only be interested in getting the contract and you staying in it so far that you can't back out. However, we backed out after 6 months of a contract and complete nightmare ... and will not use again Arq. Ignacio (Nacho) Osuna Eskenazi, who is from Guadalajara.