Now there is a local builders company that i love, i love the warehouse, the way the operate + in the near future i would like to form a partnership and maybe look at owning 37% of the business, a good percentage but then if anything could potentially go wrong? Not enough percentage to lose allot of money compared to others, plus the business structure is well thought out. Now how should i look at the price of owning that percentage of the business, plus what could the figures look like? They are privately owned.
As i do want to get into a partnership business, there are a few other companies i would like to look at making partners with in the future. Any advice? Real advice, no 
You might be best off asking this on a business forum, it's what i'd do.
In my
very limited business experience, here's some questions to ask yourself while pondering this:
Can you even afford the investment without taking a crazily 'overpriced' business loan from the bank? I say this because you're still in your very early 20's if i remember rightly...
Is the price they are asking worth the percentage? (think Dragon's Den style here - if they want £10k for 10%, is the whole business actually worth 100k?)
If you feel you might be risking a fair bit of money on this investment, is the business limited liability? (i think this is
EXTREMELY important if you own assets like a car, flat/house etc)
If you want to be a sleeping partner, can you easily just sit and make money? If you have to work within the partnership, if the likely profit worth the amount of work you might have to put in?
If i think of anything else i'll post...