TLDR: Talk to a highly experienced general contractor (GC) who builds homes. The good ones will have plenty of plans that you can edit to your heart's content. All three GCs that I interviewed immediately showed / emailed me plans they thought I would like to start from.
---
I built a house in Cape Cod (Massachusetts, United States,) a few years ago. A few things to consider:
When I started working with my GC, he had a whole filing cabinet full of designs. They weren't "open source," (as in copyrighted under GPL/MIT/Apache,) but he scanned the design we started from.
I then used (shockingly) preview on Mac to cut and paste it up to move some walls and rooms around. (Basically, we took some space out of the master bedroom to make one of the other bedrooms larger. The master bedroom still has a lot of extra space.)
He then sent my changes to a professional designer who brought the design up to something that the contractors could follow, and made the garage deeper so we had extra storage and a garage door for a riding lawn mower. In 2017, in Cape Cod, this cost me a little over $1000.
---
But, if you really want to get creative, I suggest hiring an architect. They have the experience that you, as an untrained novice, don't have. A good architect should be able to weigh your desires and give you something that'll be better than you could imagine.
Considering that redos are very expensive when building a house, spending a few thousand on an architect will be much cheaper than spending tens of thousands on a "redo" after the fact.
---
Furthermore, if there is a house you like, at least in MA, it's easy to find the dimensions online. Just google "[town name] GIS", and you will find the town's database of all homes. Enter the address (or street,) and you will be able to find room layouts (with sizes) used for assessments, and even the assessment of value for the home. These are all publicly available records.
It's also useful to pull the GIS data of any land you're planning on buying (in MA.) This will tell you who paid what for the land going back as far as the records are available. You can use this in negotiations. (I knew that my GC overpaid for the land before the 2008 crash, so I adjusted my negotiation style accordingly.)
---
I built a house in Cape Cod (Massachusetts, United States,) a few years ago. A few things to consider:
When I started working with my GC, he had a whole filing cabinet full of designs. They weren't "open source," (as in copyrighted under GPL/MIT/Apache,) but he scanned the design we started from.
I then used (shockingly) preview on Mac to cut and paste it up to move some walls and rooms around. (Basically, we took some space out of the master bedroom to make one of the other bedrooms larger. The master bedroom still has a lot of extra space.)
He then sent my changes to a professional designer who brought the design up to something that the contractors could follow, and made the garage deeper so we had extra storage and a garage door for a riding lawn mower. In 2017, in Cape Cod, this cost me a little over $1000.
---
But, if you really want to get creative, I suggest hiring an architect. They have the experience that you, as an untrained novice, don't have. A good architect should be able to weigh your desires and give you something that'll be better than you could imagine.
Considering that redos are very expensive when building a house, spending a few thousand on an architect will be much cheaper than spending tens of thousands on a "redo" after the fact.
---
Furthermore, if there is a house you like, at least in MA, it's easy to find the dimensions online. Just google "[town name] GIS", and you will find the town's database of all homes. Enter the address (or street,) and you will be able to find room layouts (with sizes) used for assessments, and even the assessment of value for the home. These are all publicly available records.
It's also useful to pull the GIS data of any land you're planning on buying (in MA.) This will tell you who paid what for the land going back as far as the records are available. You can use this in negotiations. (I knew that my GC overpaid for the land before the 2008 crash, so I adjusted my negotiation style accordingly.)