There are several factors to consider when building a profitable mining rig:

1. Choose the right cryptocurrency to mine. Some cryptocurrencies are more profitable to mine than others, depending on factors such as the current price, the difficulty of mining, and the amount of competition.
2. Choose the right hardware. Different cryptocurrencies require different hardware to mine effectively. For example, Bitcoin can be mined with ASICs (Application Specific Integrated Circuits), while Ethereum can be mined with GPUs (Graphics Processing Units). It's important to choose hardware that is both powerful enough to mine effectively and energy efficient to keep electricity costs low.
3. Consider the cost of electricity. Mining consumes a lot of electricity, so it's important to choose a location with low electricity costs.
4. Join a mining pool. Solo mining can be very difficult and may not be profitable, especially for less popular cryptocurrencies. Joining a mining pool allows you to combine your mining power with other miners and increase your chances of finding a block and earning rewards.
5. Monitor and optimize your mining rig. It's important to regularly monitor the performance of your mining rig and make adjustments as needed to optimize efficiency and profitability. This may involve tweaking your mining software, replacing hardware that is no longer performing well, or other optimization strategies.

I hope this helps give you an idea of the factors to consider when building a profitable mining rig. Below is a simply easy-to-use mining profitability calculator.

Cryptocurrency Mining Profitability Calculator

Cryptocurrency:
Crypto price ($):
Hash rate (MH/s):
Power consumed (W):
Power cost ($/kWh):
Pool fee (%):

Calculate profitability