One stone at a time and keep at it.
The image below shows a cross section of a typical CastleMagic castle wall for you to follow along with as I describe the proper modern day castle building process start to finish.
Look for stable ground to build on, natural resources to build with, and a magical setting that seems to have been created just for a medieval castle.
Bedrock or a rocky bluff can hold the weight of a castle and is great for the foundation. You should also consider the need for soil near the castle site in addition to the rock base for the castle itself. This is because you will need to be able to dig ditches for utilities and a septic drainfield system, and of course land to farm and graze the horses. So the perfect site should be a a combination of rock and dirt together. Even if you can't find both, don't let that stop you if the site is just too good to pass up. There are ways to achieve what you need that won't be the easiest, but anything can be done if you put your mind to it.
Trees and water!
Finding a site with healthy tall trees that can be harvested for lumber can make castle building easy, authentic, and reduce the time and money it takes to complete a castle. Portable sawmills can out do a lumber store if the trees are in good shape.
Castles just like to be near water and so do people. A stream with a 60 foot or more head can generate power. You need water to mix mortar and you will need a well. So check the local well records or ask the neighbors about their wells before buying land. It doesn't get much better than a view of a lake, river, or ocean when building a castle.
For the base of a castle, it is called the footing. This can be the bedrock itself or it can be created by laying out continuous horizontal steel reinforcing bars and pouring a wide concrete footing to spread the weight of the castle over normal stable soil.
Next is to build the foundation wall from the footing up to the grade level, or the normal or desired ground level. The height of the foundation wall can be zero or more depending on where you are trying to get the grade level at or where the frost level is. The foundation wall will match the base thickness of the castle walls above and doesn't have to be as wide as the footing in normal settings. The foundation wall will have both horizontal and vertical steel bars extending up and down into the foundation.
Gather your stone and get ready! Easiest way is to call a quarry and have the best stone trucked in direct. You will need a rough terrain forklift on site at all times for unloading trucks and moving and raising materials. If you are fortunate enough to have found castle rock on site, Yay!
Start with the vertical rebar grid and add the horizontal bars. Next is to add and plumb up the insulation layer. Next is to add the outer stone wall while inserting stone ties through the insulation for future connection to the inner wall. Use the insulation wall as a guide for the stone. Next switch to the inside and lay up the inside stone wall using a measuring tape to gauge your distance from the insulation layer. Lock the ties in place as you lay up the inside wall. Do not drop any mortar into the wall core as you lay up the inside stones. Final step is to pour the concrete using the double stone walls as your formwork. Repeat the process until you reach the roof and battlements.
There are small steps that are done while building the walls. You will need to install electrical conduit pipes, window and door openings, and other small items as you build the walls. Floor beams and floor planks will be placed as the walls grow.
At the base of the castle you should have a sloped stone batter to drop rocks onto to explode away from the castle on impact. A moat is a must. May be a swimming pool in disguise as a moat. A secret swimming passage from the moat to the inside pool is the way to go.
The old wooden drawbridge is a must when building a castle. Raise the drawbridge to protect you and the castle. Add a portcullis to the entrance door is another must have. And don't forget to add real flame torches to frame your grand castle entrance.
For castle builders, the best days are the stone arch days. It is best and easiest to use the same insulation boards that you are using for the walls to make the arch forms. Easy to do and light weight. After the arch form is removed, you reuse the insulation to build the walls.
The arch stones can be found by selecting through the pallets of stone or obtained as special ordered specific sizes of arch stones and keystones.
Any shape is fine. The windows are placed while the walls are being built into the insulation layer. Since the walls are so thick, it is best to use window seat walls for grand windows to allow better outside views and more fun room inside. This is where the double castle walls shrink in thickness around the window openings only. Here the walls are just a stone/insulation/stone layer in one. The surrounding thicker double layered walls with the reinforced concrete layer encase the window walls.
To top off a castle's architecture, the crown jewels are the battlements with the merlons and crenelles. The use of corbels, arches, and hidden steel reinforcing allow modern day castle builders to preserve the old time look and also insert the waterproof layer at roof levels.
At the top of the castle it is time to buckle down and install the ever so important waterproof layer from the roof under the stone slate roof deck, out under the battlements, and down the outside of the castle wall. You cannot skip this step. Note the red line in the drawing below.
Watch the video below to see the computer simulation of Castle Kalikai grow.
Kalikai castle tower plan hand drawn sketch; 1600 sq ft, three bedrooms.
Castle Kalikai computer drafted; 2800 sq ft , 4 bedroom version (4 mb file size 720x1200)