Some ideas cost more than others to implement, but the best way to assimilate that list of must have features is to visit a lot of existing homes and take notes on how features that you like are put together. You should always go to a party with a notepad and a tape measurer. When you see a kitchen/dining/living space that just fits and makes you feel comfortable; don't just compliment the owner, hang back after the party and measure off the rooms, closets, bathrooms, ceiling heights, and note how they are laid out. You can use these type of specific notes to help your architect understand what you want, or you can use those notes to help layout your own floor plan.
Another great trick for putting together an awesome home design is to visit construction sites and start talking to the tradesmen onsite. See first hand how they are doing their jobs. If you catch a friendly one, ask lots of questions ... people usually like to be the expert and blab about their business. Always take a note pad and a tape measurer because you do need specific data if you are going to design the house for yourself. If you are inexperienced, be careful to get data from many projects and talk to many different people about the same questions. You will have to combine all the different answers you get to what makes the most sense for your situation. You need to review many houses so you can learn what items you can simply copy vs. when you must engineer a solution. For example, every room has 2X4s to hold up the walls at 16" centers. You can copy that and use that same pattern no matter how big the room is. But, if you are building a floor that spans 12 feet between supports, you will need a much stronger board than if your floor only spans 8 feet. You need to look at many structures to get a feel for when you can copy and when you must do some thinking and/or research.
I built my whole house from a sketch of the floor plan on 3 sheets of 8 1/2" X 11" engineering paper. Since I erected the foundation forms, laid the re-bar, plumbing, and framed the house, I didn't need much detail at all. Most of the design was in my head, and I had the freedom to make many decisions on the fly. However, most details should be decided ahead of time, and so here is a list:
1. Dimensions and locations of all rooms, garages, closets, hallways, stairs, and the boundaries of the house. Remember to account for thickness of walls in the floor-plan. For any type of masonry exterior, the foundation should extend 5.5" beyond the outside face of the walls. The walls will be about 4.5" thick if you are using 2x4 studs for your walls.
2. Height of all rooms. Allow for at least 12" boundary space between floors. If some areas have short spans and you have only 10" floor joists, decide how you are going to match that up with areas that might require 12" joists. You can just add that couple of inches to the ceiling height of the room under the 10" joists.
3. Size and pitch of the roof. The roof should extend 18-24" beyond the walls of the house. Also, whether a hip roof or how the ridges will run. I'm partial to a simple single ridge, non-hip roof. It is easy to build and it is very efficient if you do a metal roof.
4. The location and size of all doors and windows. Be very careful with closets and bathrooms to make sure you have room to actually open the doors and pass through. Take specific measurements from an existing house to see how much space is needed for the toilet or bathtub you plan to install.
5. Location and shape of driveways, porches, and decks. Be sure to use 2x10s to create a lowered ledge in the foundation for the bottom of the garage doors to fit into. Normally you will use 2x6 lumber to form a 'brick ledge' around the rest of the house.
6. Where all the load bearing walls will be. These should rest on top of beams in your foundation or floors.
7. For a concrete foundation, location of supporting beams. The beams should be re-bar reinforce concrete that are 30-36" in depth. They should approximate a 12' x 12' grid across the foundation, but you may shift them around to match up with your load bearing walls. If building in really terrible soil, you may consider digging pier holes as well. ( Talk to neighbors and see how their foundations are doing ).
8. Location and size of any spanning beams for upper floors or across a basement. These must be strong enough to hang the floor joists off of and support the weight of your mother-in-law's pet elephant.
9. Location, size, ventilation, and entrances for any crawl spaces, basements, or storm cellars.
10. Plumbing locations. Starting with the water service inlet, and ending with the main septic line out, decide where all the lines will go and what size they should be. Check out the section on plumbing for more details. If you have any custom bath tub units that you are planning to install, get the specs ahead of time so you know exactly where the drain and pressure lines go. Also, remember to account for lines for any ice-maker, external faucets, or other appliances you might want ... and fire sprinklers too. Finally, remember to plan spaces in walls for vent pipes to be run off the drain lines up through the roof. You may have to build some 2x6 walls behind bathrooms, for example, to hide vent pipes.
11. HVAC. Make sure you have places to run ducts and air returns. Make sure you have a location in the attic to accommodate the unit and that it is near a suitable location for the condenser outside. Consider how the noise from the unit might affect the occupants and plan to locate away from bedrooms if possible.
12. Electrical. At least decide where the main breaker box is to be located. I like to have mine in the garage with the main power coming from underground. So, that means I had to run conduit from the service pole underground and then up through the edge of the foundation of the garage.
13. Appliances: plan for venting the cook-stove, clothes dryer, wood stove, or fireplace.
14. Location of water heater, emergency pressure relief line, and French drain in case it ever leaks.
15. Orientation and location of the house on the property, location of utilities and access to the property.
Here's the story on how I designed my first house:
I started by designing a tiny little garage apartment with 3 tiny bedrooms, 1 bath, a kitchenette, and a living space downstairs behind the garage. I began construction out of my garage in Houston some 200 miles away from where I ended up building the new house. I just started building door and window bucks. I ended up needing more as the design "grew", but it was a way for me to get started since I had a dry place to store them:
These are easily used later in any house design, as long as you don't change your mind on the size of the windows you want.
By getting this early start with the hammer and nail, I did lock in the width of my house when I started building roof trusses and floor joists.
These set my width at 24', but I was able to add more space to the house by building more of these than I had originally designed for. Still, I didn't want my house to look like a long barn, so I made the house 'L' shaped. The trick was to run rafters from one edge of the trusses out over a wider, but "single-story" part of the house. This gave me all the room I needed to fit a nice kitchen, dining, living, laundry, pantry, half-bath and closets downstairs. It also was perfect for having a space to put the HVAC equipment and a walk-in attic space that is accessed from the master bedroom without having to climb up a rickety ladder.
I did have to use some old high school geometry to figure out how high to make that main truss and how high to make the walls over the single story section of the house. The angle of the roof line needed to be constant as it descends over the section of the house seen to the left.