A plot plan and a reduced house plan is usually provided. These are very important items to have to make sure your home gets built the way you expect. Builders are like all sellers and will want to know you are qualified to buy. You should have a pre-qualification letter from a reputable lending institution. The most variable factor is timing and how long you will get a loan commitment as well as rate-lock.
Delays are part of the process.
You may even need temporary housing if you have sold your home. Before a house is started you may be able to make changes. Once a home is underway your options are limited. Some changes may cost extra. Be prepared to spend more than you planned.