There are a lot of variables but good thing is you should be able to get exactly what you want.

1. Interest rate. This could be a fixed rate for a set period, discounted for a set period, or tracker for a set period, or tracker for life etc.... Basically as it's an investment it's not regulated by the FSA so it's up to you what u decide to go for. Lot of people think interest rates have about peaked, so should be coming down within a year or so. Therefore a long fixed rate could tie you in at a higher rate if interest rates do go down. However fixed rates you know where you are from month to month.

2. Amount. You can get different loan-to-value amounts, but prob 85% (meaning you put down 15% deposit) is a good place to start. A 90% loan will prob cost you more in rates etc.

3. Rent ratio. They will only lend you the percentage amount as long as the rent ratios are all ok too. Better value products have 125% ratios, which means the rental income has to be 125% of the mortgage repayment. i.e. if mortgage is £100 per month then rent would need to be £125 per month. However, yields hav been slowly dropping and wether you'll get this depends on where you buy. You can get 100% deals where teh rent only has to cover the mortgage repayments, but i suspect these dont offer as good value as the 125% deals. As the risk to the bank increases so do the costs generally!

4. Interest only / repayment. If you want a bit of money each month to live off then interest only will mean smaller mortgage repayments, therefore more left over each month, but you never pay off the loan. Repayment might be best way to go for a pension fund as in 30 years the house is all yours! However, aggressive investors go for interest only as more money is avaible for further purchases

5. Also watch out for other charges i.e. arrangement fees, exit costs. Lower arrangement fees mean higher interest, but possibly more flexibility if interest rates come down and you want to get out of the deal

6. other costs. You dont pay council tax whilst it's empty, but you do pay mortgage costs! Therefore get it let asap. A letting agent will keep the nasty tenants away but take 3 weeks rent for doing the job plus 10% per month if you want them to manage the property. And dont think the tenants wont phone you up over all manner of stupid things either! Also alllow for repairs, insurance, yearly safety checks etc.

It's a lot of hard work and def not as easy as tv makes it sound, especially with uncertaintly in teh short term over house prices and interest rates. But if your in it for the long term then should see you well in the future