Hi Maggy,
This is a big subject so I´ll try to be as brief as pos.
1) I would suggest you ask your lawyer to find an architect he can recommend and work with. this will make life easy for all concerned.
2) Get your lawyer to find out first if planning consent is possible on the plot. Plano Parcial or as in the UK outline planning permission.
3) If planning is possible on the land then your lawyer needs to ask "How many m2 of build is possible". Usually in the Murcia area up to 150m2 house. Also ask how many floors 1 or 2 etc.
4) If planning is possible and you get your build size agreed in principle, DO NOT CONSIDER THIS TO BE GUARANTEED. You will find that it will take up to 2 years before the Enviro in Murcia rubber stamp it, even after 2 years of waiting they could easily say NO, as rules change during that kind of time lapse.
5) So if you´re still brave enough to continue, next buy the land and get your architect to draw up a design for submission to the town hall. It´s a good idea to look at loads of new build show houses to give you ideas. Or cut out the room shapes and sizes you would like and try and fit them together avoiding exceeding your build size.
6) The architect you choose should be willing to be the project manager to see the whole thing through to completion. He will draw up full plans and submit them to the town hall as a project (proyecto). At this point he will charge you for his time could be up to €5,000 or as low as €3,000. If you feel your architect is good don´t skimp on these fees.
7) The architect will also take funds off you for the apericador (the man in the town hall who puts your project to planning) this is usually around €4,000. - €8,000 depending on the build cost estimates obtained by the architect prior to application.
8) Here in Murcia the build costs should be between €750 - €1,000 per square metre. So a 150m2 house would cost around €150,000, this would include all fittings inc. bathrooms and kitchen etc.
9) Then you wait and wait and wait and wait then wait a bit more for 2 years.
10) If you are lucky and they say yes, you can go ahead with your architect obtaining the building licence and begin laying bricks.
11) On completion the architect will arrange for the Habitation Certificate, so he can apply for you electricity and water certificate and connection. With this done you can arrange an appointment at the Notary with your lawyer to sign title deeds (Escritura).
There will be further costs down the line - 1% here 2% there, it changes so much here in Murcia that not even your architect will be able to give you exact costs. Just make sure you have 20% in hand over the build costs to be sure you are covered.
I have not listed every stage, only the important ones and emphasised the waiting. But essentially this what is entailed in a nutshell!
I hope it helps, I can pm a good lawyer in Murcia if you would like.
Good luck
Gillespie.
PS I suggest you avoid any English project managers, they are usually con-men and will be on 10-20% and usually go to ground when a problem occurs.